Photography Calculators

Studio, storage & utilities

SD Card Capacity Calculator

Cards are sold in decimal gigabytes. Stills count is floor of (GB × 1000 / file MB). Video minutes are (GB × 8000 / Mbps) / 60 if you set a bitrate; leave bitrate at 0 for stills only. Format in the camera, leave a margin, and do not start a ceremony on the last 4 GB. A test burst of 20 RAWs tells you the real file size better than the brochure.

Inputs

Units
GB

Labelled size, e.g. 128. Not the binary GiB your computer shows after format.

MB

Average RAW or JPEG size from a test burst, not the ‘up to’ spec.

Mbps

Set 0 if you only care about stills. Otherwise the camera’s Mbps rating.

Results

Stills that fit
2,844
Video that fits
85.3min

Zero if bitrate is 0.

Recommended gear

Calculation method

Treat 1 GB as 1000 MB. Still count is the whole number of files of your average size that fit. Video minutes convert bits on the card to time: capacityGB × 8e9 bits, divided by bitrate Mbps × 1e6, then by 60 (equivalently GB×8000/Mbps/60). Zero if you set bitrate to 0. A 128 GB card at 45 MB RAWs is 2844 stills; at 200 Mbps that is about 85 minutes of video. Containers, dual-slot mirroring and the camera’s reserve are not subtracted.

Exact formula

stillCount = floor(capacityGB×1000 / fileSizeMB). videoMinutes = capacityGB×8000 / bitrateMbps / 60 if bitrate>0 else 0. Limits: Decimal GB (1000, not GiB); camera overhead, dual-slot mirroring, format waste, audio mux and VBR omitted — real minutes run shorter.

Speed class

Capacity is not sustain rate. V30/V60/V90 and CFexpress ratings are about dropped frames, not how many JPEGs fit.

Format in camera

A card formatted on a PC can still throw ‘cannot record’. Format in the body you will shoot, every job.

Frequently asked questions

Why does the computer show 119 GB?

OS tools often use 1024. The label is 1000. This calculator follows the label so it matches the shop sticker, not Finder.

RAW+JPEG?

Add the two sizes for file size, or you will count twice as many frames as you can actually shoot.

Dual slot backup?

If slot 2 mirrors slot 1, you do not get extra capacity. If it overflows, you do. Set the camera mode before you trust this number.

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