Astrophotography Storage Calculator

An Astrophotography Storage Calculator estimates how much capacity an imaging session will consume during capture, processing, and backup. For existing equipment, multiply the mean size of representative files by the planned frame count. For uncompressed data, calculate payload from image dimensions, channels, and stored bit depth, then add format overhead, processing expansion, planning headroom, and complete protected copies.

Key Takeaways

• Use the arithmetic mean of representative files to estimate expected aggregate storage.
• Keep the median, a high-percentile value, and the largest sample for different planning decisions.
• Calculate capture data, processing workspace, planning headroom, and protected copies separately.
• Distinguish decimal GB and TB from binary GiB and TiB.
• FITS size depends on padded headers, padded data units, extensions, and possibly compression—not only image dimensions.
• A calculated write rate is an arithmetic minimum, not proof that a card or drive is camera-compatible.

This guide explains how to estimate RAW, FITS, video, calibration, processing, mosaic, backup, write-speed, transfer-time, and multi-night storage without treating megapixels or advertised drive capacity as complete answers.

Method note: Numerical tables and worked examples were generated from the formulas shown in this guide and checked in a separate calculation pass. Binary file values use MiB and GiB; manufacturer storage capacities commonly use decimal GB and TB. The calculations are planning analyses rather than hands-on tests of particular cameras, storage cards, drives, capture programs, or processing applications.

How Does the Astrophotography Storage Calculator Work?

Three calculation methods cover most astrophotography workflows.

Method	Best use	Core calculation
Measured-file method	Camera RAW, compressed FITS, proprietary files	Representative mean file size × planned count
Array method	Uncompressed FITS or known image arrays	Width × height × channels × stored bits ÷ 8
Bitrate method	Planetary video or continuous recording	Bitrate × duration ÷ 8

The calculator’s direct estimate should use only the inputs actually entered. The additional formulas in this guide extend that result to processing workspace, headroom, backup copies, transfer time, and multi-volume capture planning.

Which File-Size Statistic Should You Use?

Use the mean for expected aggregate capacity, the median for a typical individual file, and a high-percentile or conservative value when running close to a card or drive limit.

Measured-File Method

For variable-size formats, capture a representative sample using the intended:

• resolution;
• crop or region of interest;
• bit depth;
• compression;
• file format;
• camera mode;
• binning;
• scene type.

Record each file size in bytes.

Calculate the arithmetic mean:

Mean sample file size
= total logical bytes in the sample
÷ sample file count

Then estimate expected storage:

Expected storage
= mean sample file size
× planned file count

Also record:

• median file size: a useful description of a typical individual file;
• 90th or 95th percentile: a conservative value for session planning;
• largest representative file: useful for stress testing.

Why the Mean Is Better for Aggregate Storage

The total size of a collection is the sum of its files. When a representative sample reflects the intended capture conditions, its arithmetic mean directly estimates the expected bytes per future file.

A median can understate aggregate storage when a minority of files are substantially larger than the rest. It remains valuable for describing a typical file because it is less sensitive to isolated extremes.

Which Statistic Fits Which Decision?

Statistic	Appropriate use	Main limitation
Mean observed file size	Expected aggregate storage	Sensitive to unrepresentative large or small samples
Median observed file size	Typical individual file	May underestimate total bytes in a skewed distribution
High-percentile file size	Conservative session or card planning	Requires a sufficiently large sample
Largest representative file	Capacity stress test	May overestimate ordinary storage
Manufacturer estimate	Initial comparison	May use different scenes, settings, firmware, or rounding

For a card that will remain comfortably below capacity, the sample mean plus documented headroom may be sufficient. For a card expected to approach its limit, use a high-percentile or deliberately conservative file size.

How Do You Estimate an Uncompressed Image?

For a rectangular uncompressed image array:

Payload bytes
= image width
× image height
× channel count
× stored bits per sample
÷ 8

For a monochrome 6,000 × 4,000 image stored in a 16-bit container:

6,000 × 4,000 × 1 × 16 ÷ 8
= 48,000,000 bytes

That is:

48.0 MB
or approximately 45.8 MiB

This formula calculates array payload. It does not include:

• file headers;
• previews;
• metadata;
• file-format padding;
• file-system allocation;
• overscan;
• additional HDUs;
• compression;
• software-specific data structures.

How Does Bit Depth Affect Storage?

Theoretical uncompressed payload grows in direct proportion to the stored bits per sample.

16-bit data use twice the payload of 8-bit data.

32-bit data use twice the payload of 16-bit data.

The camera’s analog-to-digital converter depth does not always equal the physical number of bits allocated to each saved sample.

Possible implementations include:

• tightly packed 12-bit values;
• compressed 12-bit or 14-bit values;
• camera samples placed in a 16-bit container;
• processing data converted to 32-bit floating point;
• RGB working files containing three complete channels.

Nikon’s official NEF RAW documentation lists 12-bit and 14-bit recording together with lossless-compressed, compressed, and uncompressed modes. Its memory-card capacity table also notes that reported file sizes are approximate and can vary with the recorded scene.

Theoretical Single-Frame Payload

The following original table shows mathematical array payload before headers, padding, previews, or compression.

The packed 12-bit column is not a FITS BITPIX=12 calculation. Standard FITS image arrays do not use BITPIX=12.

Pixel count	Tightly packed 12-bit	16-bit container	32-bit float	100 frames at 16-bit
6 MP	8.6 MiB	11.4 MiB	22.9 MiB	1.12 GiB
12 MP	17.2 MiB	22.9 MiB	45.8 MiB	2.24 GiB
24 MP	34.3 MiB	45.8 MiB	91.6 MiB	4.47 GiB
36 MP	51.5 MiB	68.7 MiB	137.3 MiB	6.71 GiB
60 MP	85.8 MiB	114.4 MiB	228.9 MiB	11.18 GiB

The table does not predict the RAW size of a particular camera. Proprietary compression, previews, metadata, and storage layout can produce materially different files.

What Is the Difference Between MB, MiB, GB, and GiB?

Decimal and binary units use different divisors.

The National Institute of Standards and Technology defines:

1 MB  = 1,000,000 bytes
1 MiB = 1,048,576 bytes

1 GB  = 1,000,000,000 bytes
1 GiB = 1,073,741,824 bytes

1 TB  = 1,000,000,000,000 bytes
1 TiB = 1,099,511,627,776 bytes

A drive sold as:

1 TB

contains approximately:

931.3 GiB

before formatting, system partitions, reserved areas, or existing files are considered.

Neither value is incorrect when its unit is stated accurately. Confusion occurs when decimal and binary quantities are mixed without labeling them.

Recommended Calculator Output

A trustworthy calculator should show:

• exact bytes;
• decimal MB, GB, or TB;
• binary MiB, GiB, or TiB;
• the conversion basis used.

What Is Logical File Size Versus Space Used on Disk?

A file can have two relevant sizes.

• Logical file size: the number of bytes contained in the file.
• Allocated size: the physical space reserved for it by the file system.

File systems allocate storage in whole blocks or allocation units. A file that uses only part of its final unit still occupies the complete unit.

Therefore:

Space used on disk
may exceed
the sum of logical file bytes

The difference is usually small for large RAW or FITS frames. It can become more noticeable when a project contains many small files such as:

• logs;
• previews;
• thumbnails;
• database entries;
• sidecar files;
• scripts;
• masks;
• temporary records.

Use logical bytes for image-format calculations. Use measured allocated usage when planning the capacity of the actual volume.

How Do You Calculate a FITS File Size?

FITS stores information in Header/Data Units, or HDUs. Each header and each data section is padded separately to a multiple of 2,880 bytes.

NASA’s FITS Primer explains that every header record occupies 80 characters and that headers and data units are stored in 2,880-byte blocks.

FITS Header Size

Count every header card through and including the END card.

Unpadded header bytes
= header card count × 80

Then pad the header:

Padded header bytes
= 2,880
× ceiling(
    unpadded header bytes
    ÷ 2,880
  )

For example, a header containing 40 cards has:

40 × 80
= 3,200 unpadded bytes

It therefore occupies:

2 × 2,880
= 5,760 padded bytes

Ordinary Image-HDU Data Size

For an uncompressed primary image or ordinary image extension:

Unpadded image bytes
= |BITPIX| ÷ 8
× NAXIS1
× NAXIS2
× additional axis lengths

For a two-dimensional image:

Unpadded image bytes
= |BITPIX| ÷ 8
× NAXIS1
× NAXIS2

Then pad the data:

Padded data bytes
= 2,880
× ceiling(
    unpadded image bytes
    ÷ 2,880
  )

Generalized Extension-HDU Data Size

For a generalized uncompressed extension containing PCOUNT and GCOUNT, the NASA FITS extension rules define the unpadded data size as:

Unpadded HDU data bytes
= |BITPIX| ÷ 8
× GCOUNT
× (
    PCOUNT
    + product of all NAXISn values
  )

For an ordinary image extension:

GCOUNT = 1
PCOUNT = 0

The expression then reduces to the standard image-array calculation.

PCOUNT has extension-specific meaning. In a binary table it can include supplementary data such as a heap used by variable-length arrays. It should not be interpreted as an image dimension.

Total HDU and File Size

For one HDU:

HDU bytes
= padded header bytes
+ padded data bytes

For a multi-HDU FITS file:

FITS file bytes
= sum of all padded HDU sizes

Compressed FITS Files

Compressed-image FITS files may use specialized extensions or binary-table structures. Their physical size depends on the stored compressed content and associated HDUs.

Do not estimate a compressed FITS file solely from:

width × height × uncompressed BITPIX

Measure representative compressed files or inspect the actual HDU structure.

FITS Calculation Limits

The basic formula may not describe every file exactly when it includes:

• compressed-image extensions;
• binary tables;
• variable-length arrays;
• heaps;
• multiple image planes;
• masks;
• checksums;
• overscan;
• thumbnails;
• application-specific extensions.

A FITS file-size calculator should label whether it is estimating an ordinary uncompressed image HDU or reading a complete existing file structure.

Which Estimate Is Better: Theoretical or Measured?

Use a theoretical calculation before representative data exist. Replace it with measured values when the actual capture mode becomes available.

Method	Advantages	Limitations
Theoretical array calculation	Transparent; useful before equipment is available	Omits compression and format-specific overhead
Mean observed file size	Best simple estimate of expected aggregate bytes	Requires a representative sample
Median observed file size	Describes a typical individual file	Can underestimate a skewed total
High-percentile file size	Safer near capacity limits	Needs enough sample files
Largest representative file	Useful stress-test value	May overstate normal use
Manufacturer estimate	Quick starting reference	May use different settings or test scenes

The Four-Bucket Storage Ledger

Original framework: The Four-Bucket Storage Ledger separates files by their role so that capture-only capacity is not mistaken for complete project storage. It is a planning framework rather than a storage-industry standard.

Calculate four buckets:

1. Original capture dataset
2. Calibration and support products
3. Processing workspace
4. Complete protected copies

Bucket 1: Original Capture Dataset

Include every newly captured file counted as part of the project:

• light frames;
• dark frames;
• flat frames;
• bias or dark-flat frames;
• focus tests;
• framing tests;
• plate-solving frames;
• retained rejects;
• capture logs;
• video segments.

Calculate groups independently when file sizes differ:

Capture-dataset bytes
= Σ(
    mean or conservative group file size
    × group frame count
  )

Bucket 2: Calibration and Support Products

Distinguish newly captured calibration data from existing shared libraries.

ESO documentation, such as the FORS2 calibration reference, separates bias, dark, sky-flat, lamp-flat, and science data by purpose.

Use three labels:

Newly captured project calibration
Existing shared calibration library
Archived library copy

Do not charge the same shared library to every project’s newly generated total. It still consumes physical archive capacity and should be counted in the library’s own storage plan.

Bucket 3: Processing Workspace

Possible processing products include:

• master calibration frames;
• calibrated lights;
• cosmetic-corrected lights;
• debayered or demosaiced images;
• registered frames;
• normalization data;
• drizzle support files;
• integrated masters;
• rejected-pixel maps;
• masks;
• previews;
• temporary databases;
• exported TIFF, PNG, JPEG, or other deliverables;
• application cache and scratch data.

Only count products the workflow retains or generates at peak. Do not assume temporary data are negligible without measuring them.

Bucket 4: Complete Protected Copies

Define whether the entered copy count includes the active or primary copy.

In this guide:

Total complete-copy count
= primary or active copy
+ complete backup copies

A three-copy plan means:

1 primary copy
+ 2 additional complete copies
= 3 complete copies total

Therefore:

Physical footprint
= protected project size
× total complete-copy count

When the user enters only additional backups:

Total complete-copy count
= 1 + additional backup count

Incremental, compressed, deduplicated, versioned, or snapshot-based backup systems may use a different physical amount. Estimate those systems from their measured behavior rather than pretending every backup is a full independent copy.

How Much Can Processing Expand the Data?

Processing storage can exceed capture storage because the data type, channel count, image dimensions, and number of retained versions can increase.

The following original table uses a 26-megapixel image and shows uncompressed array payload.

Representation	Bytes per original pixel	Approximate payload
Monochrome or mosaic, 16-bit integer	2	49.6 MiB
Monochrome, 32-bit float	4	99.2 MiB
RGB, 16-bit per channel	6	148.8 MiB
RGB, 32-bit float per channel	12	297.5 MiB
2× drizzle per axis, mono 32-bit	16	396.7 MiB
2× drizzle per axis, RGB 32-bit	48	1,190.2 MiB

These are mathematical array values, not guaranteed saved-file sizes.

Why Debayering Can Increase Storage

A color-filter-array capture commonly begins with one recorded value at each sensor location. A full RGB working image may store three values at every output pixel.

At unchanged image dimensions:

One 16-bit mosaic value:
2 bytes per pixel

Three 32-bit floating-point channels:
12 bytes per pixel

The theoretical array becomes six times larger before headers or compression are considered.

Why 2× Drizzle Can Require About 4× the Pixels

A 2× drizzle scale doubles both dimensions:

New width
= original width × 2

New height
= original height × 2

Therefore:

New pixel count
= 4 × original pixel count

At unchanged channel count and data type, array payload also becomes approximately four times larger.

“2× drizzle” does not mean only twice the storage.

Worked Project Example: 26 MP Monochrome Data

This example is calculation-based and does not describe a tested camera.

Capture Assumptions

Resolution:
26 megapixels

Stored capture array:
16-bit monochrome

Approximate frame payload:
49.6 MiB

Light frames:
240

Dark frames:
40

Flat frames:
50

Bias or dark-flat frames:
100

Original Capture Dataset

Frame group	Count	Approximate payload per frame	Storage
Lights	240	49.6 MiB	11.62 GiB
Darks	40	49.6 MiB	1.94 GiB
Flats	50	49.6 MiB	2.42 GiB
Bias or dark flats	100	49.6 MiB	4.84 GiB
Capture-dataset total	430		20.82 GiB

Processing Assumptions

The workflow retains:

• 240 calibrated 32-bit light frames;
• 240 registered 32-bit light frames;
• 4 GiB of masters, integrations, masks, logs, previews, and other retained products.

Calibrated lights
= 240 × 99.2 MiB
≈ 23.25 GiB

Registered lights
= 240 × 99.2 MiB
≈ 23.25 GiB

Estimated Peak Logical Data

Capture dataset:
20.82 GiB

Calibrated lights:
23.25 GiB

Registered lights:
23.25 GiB

Other retained products:
4.00 GiB

Estimated peak logical data
≈ 71.32 GiB

Headroom is not another file category. It is added after logical project data have been estimated.

Using 20% project-relative headroom:

Working capacity target
= 71.32 × 1.20
≈ 85.58 GiB

If the reserved project is kept as three complete copies in total—including the primary working copy:

Physical footprint
= 85.58 × 3
≈ 256.74 GiB

This example does not include file-system allocation differences, operating-system requirements, or unrelated data already stored on the devices.

How Should You Add Planning Headroom?

This guide defines headroom as a percentage of the estimated peak logical project size.

Capacity target
= estimated peak logical data
× (1 + headroom fraction)

For 20% project-relative headroom:

Capacity target
= estimated peak logical data × 1.20

This does not mean that 20% of the resulting capacity target remains free.

If the estimate is exact:

Unused fraction of capacity target
= 0.20 ÷ 1.20
≈ 16.7%

Project-Relative Headroom Bands

The following original bands are planning aids, not storage-industry requirements.

Headroom added relative to estimated peak data	Planning interpretation
Below 10%	Fragile; little tolerance for variation
10–20%	Limited allowance
20–35%	Practical allowance for a defined workflow
Above 35%	Greater flexibility for expansion or retained intermediates

Planning for a Desired Free-Space Percentage

A different formula is required when the goal is to keep a specified portion of the final usable capacity free:

Required usable capacity
= estimated peak logical data
÷ (1 − desired free-space fraction)

For a 71.32 GiB project with a requirement that 20% of the usable capacity remain free:

Required usable capacity
= 71.32 ÷ 0.80
≈ 89.15 GiB

Do not mix these two statements:

Add 20% relative to the project

and:

Leave 20% of the final capacity free

They describe different capacity targets.

What Is the Storage Expansion Ratio?

The storage expansion ratio compares peak logical working data with the original capture dataset.

Capture-dataset expansion ratio
= estimated peak logical working data
÷ original capture-dataset size

In this guide, the original capture dataset includes newly captured:

• lights;
• calibration frames;
• tests;
• retained rejects;
• associated capture files counted in the project.

For the worked example:

71.32 GiB ÷ 20.82 GiB
≈ 3.43

The processing workflow reaches about 3.4 times the original capture-dataset size before project-relative headroom or backup copies are added.

If the denominator contains only light frames, label the output explicitly:

Light-frame expansion ratio

Do not compare expansion ratios from different projects unless their denominators use the same definition.

What Can Increase the Ratio?

A higher ratio can result from:

• 32-bit processing;
• retained calibrated files;
• retained registered files;
• RGB expansion;
• drizzle;
• mosaics;
• normalization data;
• multiple processing versions;
• large temporary caches.

A lower ratio can result from:

• compressed capture;
• monochrome processing;
• deletion of reproducible intermediates;
• no drizzle;
• smaller caches;
• processing directly from source files.

A low ratio is not automatically better. Removing every intermediate can reduce storage while making reprocessing or troubleshooting slower.

How Do You Calculate a Multi-Night or Multi-Filter Project?

Calculate each acquisition group independently.

Project capture bytes
= Σ(
    group file size
    × group file count
  )

Create separate groups when any of these change:

• camera;
• resolution;
• filter;
• exposure length;
• binning;
• crop or region of interest;
• compression;
• file format;
• mosaic panel;
• frame type;
• recording night.

Multi-Filter Planning Table

Group	Representative size	Planned count	Storage
Luminance lights	S₁	N₁	S₁ × N₁
Red lights	S₂	N₂	S₂ × N₂
Green lights	S₃	N₃	S₃ × N₃
Blue lights	S₄	N₄	S₄ × N₄
Narrowband lights	S₅	N₅	S₅ × N₅
Calibration groups	varies	varies	group sum

Do not use one average file size when the capture groups have materially different dimensions, channel structures, or compression behavior.

Mosaic Projects

For similar panels:

Mosaic capture
≈ capture per panel
× panel count

Then account for:

• overlap;
• panel-specific rejected frames;
• separate panel integrations;
• reprojection;
• full-resolution assembled canvas;
• edge masks;
• gradient correction;
• alternate rotations;
• temporary mosaic databases.

The assembled mosaic can be substantially larger than one panel because its final canvas spans multiple panel dimensions.

Use the Camera Field of View Calculator to estimate panel coverage before converting the plan into storage.

How Many Storage Volumes Are Required?

When one card, SSD, or other volume cannot hold the planned capture:

Required volume count
= ceiling(
    planned capture bytes
    ÷ usable bytes per volume
  )

Use usable capacity after formatting, reserved space, and existing files—not the advertised label alone.

Example

Suppose:

Planned capture:
420 GB

Usable capacity per volume:
190 GB

Required volume count
= ceiling(420 ÷ 190)
= 3 volumes

The arithmetic does not account for the operational cost of changing media.

Also consider:

• swap time;
• weather exposure;
• dropped or mislabeled cards;
• file-numbering changes;
• incomplete final files;
• duplicated test captures;
• verification before reuse;
• handling media in darkness.

For remote or unattended imaging, a larger single storage pool may reduce operational risk, but it also concentrates more data on one device until another verified copy exists.

How Many Complete Files Fit on a Card or Drive?

Use available logical bytes and a conservative file-size value.

Maximum complete files
= floor(
    usable available bytes
    ÷ planned bytes per file
  )

For variable-size files, use:

• a high-percentile measured size;
• the largest representative sample;
• another documented conservative value.

Do not use the median alone when the result would fill the device close to its limit.

Example

Suppose:

Usable available capacity:
119 GiB

Conservative file size:
52 MiB

Maximum complete files
= floor(
    119 × 1,024
    ÷ 52
  )

= 2,343 files

A practical plan should stop below this theoretical maximum because the device may also contain:

• directory records;
• logs;
• databases;
• previews;
• sidecar files;
• reserved space;
• unrelated files.

How Do You Estimate Video Storage?

Use bitrate when the recording mode is specified as a data rate.

Storage bytes
= bitrate in bits per second
× duration in seconds
÷ 8

For decimal megabits per second:

1 Mb/s
= 1,000,000 bits per second

Therefore:

Storage in decimal GB
= bitrate in Mb/s
× duration in seconds
÷ 8
÷ 1,000

For binary GiB, calculate bytes first:

Storage in GiB
= total bytes
÷ 1,073,741,824

Do not confuse:

Mb/s  = megabits per second
MB/s  = decimal megabytes per second
MiB/s = binary mebibytes per second

Use the manufacturer’s documented bitrate or measure real folder growth. Sensor ADC depth is not the same as encoded video bitrate.

How Do You Estimate Required Write Speed?

Capacity and write performance are separate requirements.

Arithmetic Average File Rate

Average write rate
= file size
÷ time between file starts

For a 100 MB file generated every two seconds:

100 MB ÷ 2s
= 50 MB/s

Generated-Data Rate

For a complete run:

Generated-data rate
= total bytes generated
÷ total elapsed capture time

This is useful when file timing varies or several data streams are written together.

Label the calculated result as:

Minimum arithmetic average

It is not a guaranteed compatible storage speed.

Why the Average Is Not Enough

The recording system may also need to handle:

• burst writes;
• camera-buffer recovery;
• metadata writes;
• file creation overhead;
• preview generation;
• simultaneous guide or log data;
• temperature-related throttling;
• performance changes as media fill;
• host-interface limits;
• firmware requirements.

The SD Association Speed Class reference explains that its speed-class markings indicate minimum sequential write performance under specified conditions.

A printed peak read or write number does not prove sustained performance inside a particular camera.

Use the camera manufacturer’s supported-media requirements as the primary compatibility reference, then test the exact camera, firmware, card, reader, cable, and capture mode.

How Long Will Copying the Project Take?

Ideal transfer time is:

Transfer time
= total bytes
÷ measured end-to-end transfer rate

For 500 decimal GB at 200 decimal MB/s:

500,000 MB ÷ 200 MB/s
= 2,500 seconds
≈ 41 minutes, 40 seconds

Actual time can be longer because of:

• many small files;
• source-device limits;
• destination-device limits;
• verification;
• hashing;
• file-system overhead;
• interface sharing;
• thermal throttling;
• antivirus or indexing;
• concurrent workloads.

Measure the complete path from the real source to the real destination. A maximum interface rating is not an end-to-end transfer measurement.

The Capture–Process–Protect Check

Original framework: The Capture–Process–Protect Check separates session capacity, peak workspace, and recovery capacity before equipment or media are selected.

1. Capture: Can the Recording Device Hold the Session?

Calculate:

Lights
+ new calibrations
+ tests
+ retained rejects
+ logs or video segments

Then verify:

• usable capacity;
• generated-data rate;
• burst behavior;
• camera compatibility;
• file-system support;
• power;
• recording duration.

2. Process: Can the Working Drive Hold Peak Logical Data?

Calculate:

Estimated peak logical data
= capture files
+ retained calibration products
+ processing intermediates
+ temporary workspace estimate

Then calculate capacity separately:

Working capacity target
= estimated peak logical data
× (1 + selected headroom fraction)

Headroom is available capacity, not another data product.

3. Protect: Can the Project Be Restored?

Confirm that:

• more than one verified copy exists;
• at least one copy is physically or logically separated;
• offline or immutable protection is considered where appropriate;
• file inventories are complete;
• integrity checks have run;
• representative files open;
• restoration has been tested.

The CISA StopRansomware Guide recommends offline, encrypted backups and regular testing of backup availability and integrity.

A three-copy or 3-2-1-style plan is a resilience pattern, not a mathematical guarantee. Recovery also depends on:

• media diversity;
• geographic separation;
• version history;
• offline or immutable protection;
• encryption-key access;
• integrity checking;
• tested restoration;
• correct file selection.

How Can You Verify File Integrity?

Verify a copy before erasing the original camera card or capture drive.

Useful checks include:

• comparing file counts;
• comparing total logical bytes;
• comparing folder inventories;
• opening representative frames;
• calculating cryptographic hashes;
• checking format-specific checksums;
• performing a test restore.

The official FITS checksum convention defines the CHECKSUM and DATASUM keywords for detecting changes to FITS HDUs.

A valid checksum does not prove that:

• every intended file was copied;
• metadata are scientifically correct;
• the observation is usable;
• the backup is current;
• the project can be restored with available software.

Use checksums together with inventories and restoration tests.

Which Files Should You Keep?

There is no universal retention policy. Separate irreplaceable observations from reproducible processing products.

Usually Difficult or Impossible to Recreate

Consider retaining:

• original light frames;
• unique calibration frames;
• capture logs;
• plate-solving and session metadata;
• manual processing notes;
• final masters;
• publication files;
• unusual rejected frames that document a fault;
• scripts or settings needed to reproduce the result.

Often Reproducible

Depending on the workflow, these may be regenerated:

• calibrated lights;
• registered lights;
• temporary previews;
• caches;
• thumbnails;
• intermediate exports;
• drizzle support data;
• automatically generated databases.

Deleting reproducible data is reasonable only when:

• original captures remain intact;
• compatible calibration data are retained;
• software and settings are documented;
• recomputation time is acceptable;
• the workflow can actually be reconstructed.

Reusable Calibration Libraries

Store shared calibration libraries separately and document:

• camera;
• gain or ISO;
• offset;
• temperature;
• exposure;
• binning;
• readout mode;
• creation date;
• frame count;
• validation status.

Do not delete the only compatible calibration set because another folder has a similar name.

Storage Planning by Capture Type

DSLR or Mirrorless RAW Imaging

Use measured-file mode.

RAW size may vary with:

• compression;
• bit depth;
• crop mode;
• scene detail;
• previews;
• firmware;
• camera model.

Use the mean of a representative sample for expected aggregate storage and a high-percentile value for near-limit capacity planning.

Cooled Astronomy-Camera FITS

Use the image-array formula as an initial estimate, then inspect actual files.

Check:

• BITPIX;
• NAXIS values;
• binning;
• overscan;
• header size;
• number of HDUs;
• compression;
• capture-software extensions.

Planetary or Lunar Video

Use measured bitrate, documented bitrate, or observed folder growth.

Storage depends on:

• frame rate;
• region of interest;
• pixel format;
• bit depth;
• compression;
• container;
• dropped-frame behavior;
• duration.

Do not estimate encoded video solely by multiplying full-sensor pixels by ADC bit depth.

Star-Trail Sequences

Calculate frame count from sequence duration and cadence, then multiply by the measured file-size statistic selected for the capacity risk.

Use the Star Trail Exposure Calculator to determine frame count and sequence timing before calculating storage.

Untracked Milky Way Sessions

Include:

• sky frames;
• foreground frames;
• focus tests;
• panorama panels;
• tracked and untracked variants;
• dark frames when used;
• interval sequences.

Use the Rule of 500 Calculator for Milky Way Photography when estimating exposure duration before calculating frame count.

Common Storage-Planning Mistakes

Treating Megapixels as Megabytes

Megapixels count samples. File bytes also depend on stored bit depth, channels, packing, compression, and overhead.

Using the Median to Predict Every Aggregate Total

The median describes a typical file. Use the representative arithmetic mean for expected total bytes.

Using ADC Bit Depth as Guaranteed File Packing

A camera can compress samples or store them in a larger container.

Treating Every FITS File as One Uncompressed Image Array

FITS files can contain padded headers, multiple HDUs, tables, heaps, extensions, and compressed data.

Mixing Project-Relative Headroom with Free-Capacity Percentage

Multiplying a project by 1.20 does not leave 20% of the resulting capacity free.

Ignoring Calibration Files

Newly captured darks, flats, bias frames, dark flats, and tests can occupy substantial storage.

Calculating Only the Final Integration

Peak processing space may be dominated by calibrated, registered, debayered, normalized, or drizzled files.

Forgetting RGB Expansion

A one-sample mosaic capture can become a three-channel working image.

Treating 2× Drizzle as 2× Storage

Doubling both width and height creates four times the pixel count.

Mixing GB and GiB

A decimal-terabyte drive does not contain 1,024 GiB.

Counting Backup Space as Primary Workspace

A backup copy protects data but does not add free space to the active processing drive.

Miscounting Complete Copies

State whether the primary working copy is included in the total copy count.

Planning to Fill Media Completely

Variable files, temporary data, and unexpected captures can exceed an exact estimate.

Trusting Advertised Peak Speed

Peak interface or read speed does not guarantee sustained camera write compatibility.

Erasing Capture Media After One Unverified Copy

Verify completeness and readability before deleting the source.

Assuming Synchronization Is Automatically a Backup

Deletion, corruption, or account problems can propagate. Confirm versioning, retention, offline protection, and restoration behavior.

Troubleshooting

Problem	Likely cause	Practical response
Actual RAW total exceeds the estimate	Median or unrepresentative samples were used	Recalculate with the mean of a representative sample and a conservative upper value
FITS files exceed the array estimate	Headers, padding, overscan, extensions, tables, or compression structures were omitted	Inspect all HDUs and padded section sizes
Operating system reports less capacity than the device label	Decimal GB and binary GiB are being compared	Convert from exact bytes and label both units
A “20% reserve” leaves less than 20% free	Project-relative headroom was confused with final free-space percentage	Use the correct formula for the intended definition
Processing drive fills unexpectedly	Registered, RGB, drizzle, cache, or temporary data were omitted	Rebuild the Four-Bucket Storage Ledger
Card has capacity but capture stops	Write rate, buffer, file system, temperature, or compatibility is limiting	Check manufacturer requirements and test the full capture chain
File transfer is slower than predicted	Source, destination, verification, small files, or throttling is limiting	Measure the complete transfer path
Backup folder has a different byte count	Files are missing, altered, compressed, deduplicated, or stored differently	Compare inventories and run integrity checks
Project archive contains repeated intermediates	Retention and versioning rules are undefined	Identify irreplaceable and reproducible files
Drizzle project becomes several times larger	Both dimensions increased	Calculate the resulting pixel count, channels, and data type
Video estimate is far too high or low	Sensor payload was confused with encoded bitrate	Use documented bitrate or measured folder growth
Space used on disk exceeds summed file sizes	Allocation-unit overhead is significant	Compare logical and allocated size
Free space falls after processing cleanup	Cache or temporary files are stored elsewhere	Inspect application scratch and temporary directories
Copied FITS file will not open	Incomplete write, corruption, or format incompatibility	Verify size, checksum, HDUs, and conformance before erasing originals

Storage Purchase Checklist

Before selecting storage for an imaging project, verify:

• usable capacity;
• estimated annual growth;
• measured generated-data rate;
• camera compatibility;
• required media class;
• connection interface;
• buffer recovery;
• portability;
• environmental conditions;
• power requirements;
• warranty terms;
• encryption needs;
• active-work versus archive role;
• backup role;
• restoration plan.

Do not describe one product as universally best. Capacity, sustained speed, endurance, portability, noise, price, and recovery requirements vary by workflow.

Step-by-Step Storage Planning Workflow

Step 1: Inventory Every Capture Group

Record:

• camera;
• dimensions;
• crop or region of interest;
• bit depth;
• stored container;
• compression;
• file format;
• binning;
• filter;
• planned count.

Step 2: Measure Representative Files

Use the exact intended mode.

Record:

• sample count;
• total sample bytes;
• arithmetic mean;
• median;
• high percentile;
• largest representative file.

Step 3: Calculate the Original Capture Dataset

Add lights, newly captured calibrations, tests, logs, and retained rejects.

Step 4: Estimate Peak Logical Processing Data

Identify whether the workflow creates:

• 32-bit data;
• RGB files;
• calibrated copies;
• registered copies;
• drizzle products;
• mosaics;
• large caches;
• temporary scratch files.

Step 5: Add Headroom with an Explicit Definition

Choose either:

Project-relative headroom

or:

Desired final free-space fraction

Use the corresponding formula and label it clearly.

Step 6: Calculate Complete-Copy Footprint

Define whether the total includes the primary copy.

Estimate incremental or deduplicated backup systems separately.

Step 7: Check Volume Count

Determine whether the capture fits on one card or drive and account for operational media changes.

Step 8: Check Write and Transfer Rates

Calculate the arithmetic average, then test real burst behavior, sustained write continuity, and copy speed.

Step 9: Verify the Complete Workflow

Run a representative capture and processing sample.

Measure:

• actual aggregate file size;
• logical and allocated storage;
• temporary-file growth;
• peak project size;
• transfer duration;
• verification duration;
• restoration success.

Step 10: Save the Results

Record:

• mean capture bytes per file;
• conservative bytes per file;
• capture-dataset size;
• expansion ratio;
• headroom definition;
• complete-copy count;
• transfer rate;
• final retained archive size.

Future projects become more accurate when based on completed work from the same equipment and software.

Practical Recommendations

For a First Astrophotography Session

Measure files from the intended capture mode and leave substantial project-relative headroom.

Do not attempt to predict every processing intermediate before running a representative workflow.

For Multi-Night Deep-Sky Projects

Create a separate row for every filter, panel, frame type, and materially different file mode.

Keep capture, peak workspace, and complete-copy footprint as separate results.

For High-Resolution Cameras

Pay particular attention to 32-bit conversion, RGB expansion, drizzle, mosaics, and registered files. Capture storage may be only a fraction of the peak working requirement.

For Planetary Imaging

Measure real folder growth at the intended frame rate, ROI, format, and bit depth.

Confirm write performance with the full camera-to-storage path.

For Remote Imaging

Maintain enough local capacity to survive a delayed transfer or unavailable network.

Do not delete remote source data until another verified and restorable copy exists.

For Long-Term Archiving

Retain original captures, metadata, final masters, and enough documentation to interpret and reproduce the project.

Periodically confirm that archived media remain readable and that replacement hardware and software can still access the data.

Data Protection and Honest Workflow Disclosure

Storage planning can reduce accidental-loss risk but cannot guarantee preservation.

Maintain multiple verified copies of irreplaceable observations. Understand the difference between:

• synchronization;
• RAID;
• versioned backup;
• offline backup;
• immutable storage;
• archival media.

None of these terms alone proves that recovery will succeed.

When published images combine:

• multiple nights;
• different cameras;
• separate foregrounds;
• mosaic panels;
• replacement or synthetic content;

describe the workflow accurately when that distinction matters to the audience.

This guide provides storage-planning information, not legal, cybersecurity, archival, or professional data-recovery advice.

Practical Conclusion

The Astrophotography Storage Calculator should keep four quantities separate:

Original capture dataset
Peak logical processing data
Working capacity target
Complete-copy physical footprint

Start with measured files whenever possible:

Expected capture storage
= representative mean file size
× planned file count

For uncompressed data:

Array payload
= width
× height
× channels
× stored bits
÷ 8

Then estimate actual working data:

Estimated peak logical data
= capture dataset
+ retained processing products
+ temporary workspace

Add capacity allowance separately:

Working capacity target
= estimated peak logical data
× (1 + project-relative headroom)

Finally:

Complete-copy footprint
= protected project size
× total complete-copy count

For compressed RAW, trust representative measurements over megapixel shortcuts. For FITS, include padded HDUs and actual extensions. For video, use bitrate or measured folder growth. Before erasing original media, verify both the copy and the recovery path.

Frequently Asked Questions

How Much Storage Does a 24 MP 16-Bit Image Require?

An uncompressed one-channel 24-megapixel array contains approximately 45.8 MiB of payload. A real file may differ because of compression, headers, padding, previews, overscan, tables, or extensions.

Should I Use Mean or Median RAW File Size?

Use the arithmetic mean of a representative sample to estimate expected aggregate storage. Use the median to describe a typical individual file and a high-percentile value for conservative near-capacity planning.

How Much Extra Capacity Should I Allow?

There is no universal percentage. This guide treats 20–35% of estimated peak logical data as practical project-relative headroom for a defined workflow, not as a promise that the same percentage of the final device remains free.

Do Calibration Frames Count Toward Project Storage?

Newly captured calibration frames count toward the original capture dataset. A reusable shared library should be counted in archive capacity but does not need to be duplicated inside every project estimate.

Is a 1 TB Drive Equal to 1,024 GiB?

No. One decimal terabyte is 1,000,000,000,000 bytes, approximately 931.3 GiB before formatting and other deductions.

Does a Faster Card Increase Storage Capacity?

No. Capacity and write performance are separate. A faster card may support a higher sustained data rate, but it stores more data only when its rated capacity is also larger.

Sources

1. NASA FITS Support Office — FITS Standard
   Official FITS requirements, data structures, HDUs, headers, and extensions. Accessed August 1, 2026.

2. NASA FITS Support Office — FITS Primer
   FITS header cards, HDUs, supported data types, and 2,880-byte padding. Accessed August 1, 2026.

3. NASA FITS User Guide — Required Keywords for Extension Headers
   General extension data-size formula using BITPIX, PCOUNT, GCOUNT, and the NAXISn dimensions. Accessed August 1, 2026.

4. NASA FITS User Guide — Required Primary-HDU Keywords
   Standard image-array sizing through BITPIX and axis lengths. Accessed August 1, 2026.

5. NIST — Binary Prefixes
   Definitions of decimal and binary prefixes, including MB, MiB, GB, and GiB. Accessed August 1, 2026.

6. Nikon — NEF RAW Recording
   Official RAW compression and 12-bit versus 14-bit recording options. Accessed August 1, 2026.

7. SD Association — Speed Class
   Minimum sequential write-performance classes and host-media compatibility considerations. Accessed August 1, 2026.

8. ESO — FORS2 Calibration Data
   Examples of science, bias, dark, and flat calibration categories. Accessed August 1, 2026.

9. NASA FITS Support Office — Checksum Convention
   FITS CHECKSUM and DATASUM integrity-verification convention. Accessed August 1, 2026.

10. CISA — StopRansomware Guide
    Official guidance on offline, encrypted backups and regular integrity and restoration testing. Accessed August 1, 2026.