How much 4K video fits on a memory card depends mostly on bitrate, not the 4K label itself. Two cameras can both record 4K and produce dramatically different file sizes.
The useful formula
If the camera gives bitrate in megabits per second, a quick estimate is:
Recording minutes ≈ card size in GB × 8,000 ÷ bitrate in Mbps ÷ 60
This is an estimate. Real formatted capacity is lower than the number printed on the card, and some cameras use variable bitrate.
Approximate recording times
| Bitrate | 128GB | 256GB | 512GB |
|---|---|---|---|
| 100 Mbps | about 171 min | about 341 min | about 683 min |
| 200 Mbps | about 85 min | about 171 min | about 341 min |
| 400 Mbps | about 43 min | about 85 min | about 171 min |
Why the real number can be lower
- Formatted capacity is lower than the advertised decimal capacity.
- Variable bitrate recording changes with image complexity.
- Audio and metadata add a small amount of data.
- Cameras may reserve space for file-system overhead.
Do not confuse capacity with speed
A 512GB card may hold a lot of footage but still be too slow for a demanding recording mode. Capacity tells you how much data fits. Speed class tells you whether the card can write the stream reliably.
Read the guide to V30, V60, V90, UHS-I, and UHS-II cards.
Product-specific recording examples
- Canon EOS R50 4K recording time on 32GB, 128GB, and 512GB cards
- Sony ZV-E10 II card requirements for recording modes up to 600 Mbps
- DJI Osmo Pocket 3 4K/120 slow-motion recording limit
- GoPro HERO13 Black microSD speed and capacity requirements
Bitrate is the missing number
If you know the resolution but not the bitrate, you still do not know the file size. Bitrate is what lets you turn a recording mode into a useful storage estimate.