Video Data Rate Calculator

These two calculators handle the math every video shooter ends up doing. You can figure out how much record time a card gives you at a given bitrate, or what bitrate a recording works out to from its size and length. They’ll also tell you the write speed your card needs and which card class covers it.

Megabits vs Megabytes

Cameras list video bitrates in megabits per second (Mbps) and memory cards list their speeds in megabytes per second (MB/s), which is where most people get tripped up. One byte is eight bits, so to go from the camera spec to the card spec, divide by eight.

Camera bitrate	Written to the card	Minimum card
100 Mbps	12.5 MB/s	V30
200 Mbps	25 MB/s	V30
400 Mbps	50 MB/s	V60
600 Mbps	75 MB/s	V90
1,200 Mbps	150 MB/s	CFexpress
2,600 Mbps	325 MB/s	CFexpress

The V rating is just a guaranteed minimum sustained write speed, so V30 is 30 MB/s, V60 is 60 MB/s and V90 is 90 MB/s. A V30 card covers you up to 240 Mbps on paper, but I’d leave some headroom and step up a class if you’re close to the limit. Because UHS-II SD tops out around 300 MB/s, anything above that needs CFexpress.

What Is Video Bitrate?

Video bitrate is just how much data your camera writes to the card every second while you’re recording. A higher bitrate packs more information into each frame, which generally gives you cleaner footage with less banding in skies, better shadow detail, and fewer compression artifacts in fast motion. It also means bigger files and needing a faster card.

File size depends only on bitrate and time, not resolution, so 100 Mbps 1080p produces the exact same file sizes as 100 Mbps 4K. When people say they need bigger cards “for 4K,” what they really need is just room for 4K’s higher bitrate.

H.264 vs H.265: What Bitrate Do You Actually Need?

The same resolution and frame rate can look very different depending on the codec. Since H.265 (HEVC) is more efficient than H.264, a rough rule of thumb is you can get close to H.264’s quality at around half the bitrate. On a 128GB card, that’s the difference between getting about 28 minutes at 600 Mbps and 57 minutes at 300 Mbps.

The catch is on the editing side, since H.265 is harder to decode and can bog down older computers without hardware acceleration or proxies. If your machine handles H.265 smoothly, it’s the better use of card space, but if it doesn’t, stick with H.264 and plan for bigger cards.

All-Intra codecs (like Sony’s XAVC S-I or Canon’s ALL-I) are usually the modes that need V90 or CFexpress. Because they compress each frame separately, they’re easier to edit, but they need a much higher bitrate.

Real Camera Examples

• To record XAVC S-I at 600 Mbps, which is 75 MB/s, on the Sony A7S III and Sony FX3, you’ll need a V90 SD card or CFexpress Type A.
• You need CFexpress Type B for the Canon R5, since it records 8K RAW at up to 2,600 Mbps, which is 325 MB/s, and that’s beyond UHS-II.

Slow Motion Is the Exception

High frame rate and slow motion modes, like Sony’s S&Q, can need a faster card than the listed bitrate suggests because the spec sheet is sometimes based on the slowed-down playback file rather than how fast data actually hits the card while you’re recording. Instead of dividing by eight for these modes, just follow the camera maker’s card requirements, which I list in my camera-specific memory card guides.

Why Your Card Records Less Than the Calculator Says

Expect real record times to be a few percent shorter than the calculated number, so don’t plan a shoot right to the last minute of a card. Card makers measure capacity in decimal gigabytes (1 GB = 1,000,000,000 bytes), and the calculator does too, but after formatting, cameras lose a little space to the file system. Some also show capacity in binary units, which makes the number look smaller again.

See my guides to the fastest SD cards, CFexpress Type A cards and CFexpress Type B cards for tested write speeds on real cards, and if you’re setting shutter speed for video, my shutter angle calculator handles that.