Memory Card Capacity Calculator

How this is calculated

FILE SIZE FOLLOWS FROM RESOLUTION AND FORMAT, and for RAW it is close to arithmetic. An uncompressed 14-bit RAW is one pixel times 14 bits, so a 24 megapixel sensor produces about 42 MB a frame - megapixels multiplied by bit depth and divided by 8. Compressed RAW typically lands near 1.1 MB per megapixel, which is roughly 60% of uncompressed and about 26 MB for the same sensor. ⚠️ JPEG SIZES ARE GENUINELY VARIABLE AND THE FIGURE HERE IS ONLY A GUIDE. A JPEG's size depends on the quality setting and on how complex the scene is - a picture of a blank wall compresses to a fraction of what a forest full of leaves does, on the same camera with the same settings. Around 0.3 MB per megapixel is a fair average for a fine-quality JPEG, but individual frames vary by a factor of several either way. RAW barely varies, because it is close to raw sensor data. ⚠️ VIDEO IS NOT IN THE SAME LEAGUE AND IT IS WHAT ACTUALLY FILLS CARDS. At 100 Mbps, half an hour of 4K takes 22.5 GB - about the same as 850 compressed RAW frames from a 24 megapixel camera. If you shoot any video at all it dominates the card, and a photographer who has never run out of space can be surprised the first time they record a few clips. The tool subtracts the video first for exactly that reason. CARD CAPACITY IS DECIMAL AND FORMATTING TAKES A LITTLE. A 128 GB card holds 128 billion bytes, and the file system's own structures use a small share of that, so the space available to you is slightly under the number on the label. It is a percent or so rather than the 7% gap you see quoted for drives, and it is not the reason a card fills sooner than expected - that is almost always video. BURST SHOOTING IS LIMITED BY THE BUFFER AND THE WRITE SPEED, NOT THE CAPACITY. A card with plenty of room can still stop a burst dead if it cannot absorb frames fast enough, which is a completely separate specification from size - and for 4K video there is usually a minimum sustained write speed the camera requires. Running out of speed and running out of space feel similar in the moment and have nothing to do with each other. ⚠️ ONE BIG CARD IS NOT OBVIOUSLY BETTER THAN SEVERAL SMALL ONES. Cards fail, and everything on a failed card goes at once, so a single 512 GB card is a single point of failure for an entire trip. Many photographers deliberately shoot smaller cards and change them, which is a backup strategy rather than a capacity decision - and no calculator can weigh it for you. SHOOTING BOTH RAW AND JPEG WRITES BOTH FILES. If your camera is set to RAW+JPEG, add the two figures together; this tool counts one format at a time.

Common questions

How big is a RAW file?

For uncompressed RAW it is close to pure arithmetic: one value per pixel at the sensor's bit depth, so 14-bit uncompressed is 1.75 bytes a pixel and a 24 megapixel sensor produces about 42 MB a frame. Compressed RAW - which is what most cameras write by default - lands near 1.1 MB per megapixel, roughly 60% of that, or about 26 MB for the same sensor. The useful consequence is that RAW barely varies between frames, because it is close to raw sensor data. What you get on a blank wall is about what you get on a forest.

Why do my JPEGs vary so much in size?

Because JPEG compression works by discarding detail the eye is unlikely to miss, so how much it can discard depends entirely on the scene. A photograph of a blank wall or a clear sky compresses to a fraction of what a forest full of leaves does, on the same camera at the same quality setting - a factor of several between individual frames is completely normal. The 0.3 MB per megapixel here is a fair average for fine quality, but it is an average in a way that the RAW figures are not, and a card of JPEGs will not fill at a steady rate.

Why does video fill my card so fast?

Because it is not remotely in the same league as stills, and the comparison is worth internalising. At 100 Mbps, half an hour of 4K takes 22.5 GB - about the same as 850 compressed RAW frames from a 24 megapixel camera. Put another way, a minute of 4K costs you roughly what 28 RAW photographs do. A photographer who has never come close to filling a card can be genuinely surprised the first time they record a few clips on a shoot, which is why this tool subtracts the video before counting frames rather than after.

Does a 128 GB card really hold 128 GB?

Almost. Card capacity is quoted in decimal gigabytes - 128 billion bytes - and the file system's own structures use a small share of that, so the space actually available is slightly under the label. It is a percent or so, not the roughly 7% gap you see quoted for hard drives, because that gap is about decimal-versus-binary units rather than formatting. Either way it is not why a card fills sooner than expected. That is almost always video, and occasionally shooting RAW+JPEG without realising both files are being written.

Will a bigger card let me shoot longer bursts?

No, and the two get confused constantly. Burst length is limited by the camera's buffer and by how fast the card can absorb data - a completely separate specification from how much it holds. A card with hundreds of gigabytes free can still stop a burst dead if its sustained write speed cannot keep up, and most cameras specify a minimum sustained write speed for 4K recording that a slow card will fail regardless of capacity. Running out of speed and running out of space feel identical in the moment and have nothing to do with each other.

Should I buy one big card or several small ones?

That is a backup question rather than a capacity one, and it is worth deciding deliberately. Cards do fail, and when one does everything on it goes at once - so a single 512 GB card is a single point of failure for an entire trip, while four 128 GB cards mean a failure costs you a quarter of it. Plenty of working photographers deliberately shoot smaller cards and change them for exactly this reason, accepting the inconvenience as insurance. No calculator can weigh that trade for you, but it should be a choice rather than an accident.

What if I shoot RAW and JPEG together?

Then the camera writes both files and you should add the two figures together - this tool counts one format at a time. On a 24 megapixel camera that is roughly 26 MB of compressed RAW plus around 7 MB of fine JPEG, so about 33 MB a frame rather than 26. It is a common setting to have enabled without noticing, and it is one of the few things besides video that meaningfully changes how fast a card fills. Run the tool twice and add the results if you want the exact figure.

Take it further with AI

Copy this into ChatGPT or Claude with your own numbers filled in. It hands over the figures this calculator worked out, so the answer is built on real arithmetic instead of a guess.

I used the Memory Card Capacity Calculator at https://www.bfcbrilliance.com/tools/photo-storage-capacity-calculator.

What I entered:
- Card size (GB): ___
- Camera resolution (MP): ___
- Format you shoot: ___
- Minutes of video also on the card (min): ___
- Video bitrate (Mbps): ___

What it calculated:
- Photos that fit alongside the video: ___
- Size of one frame: ___
- Space the video takes: ___
- That video, in frames it cost you: ___
- Photos if the card held nothing else: ___

Use those figures as given — they are already worked out, so please don't recalculate or estimate your own. Help me turn them into a plan: what to buy or do, in what order, roughly what it should cost, and the mistakes people most often make with this job.

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