How much video fits on an SD card?
The math is simple once you know the bitrate: time = card size × 8 × 1000 ÷ bitrate. A 128 GB card at 100 Mbps (GoPro 4K): 128 × 8000 ÷ 100 = 10,240 seconds ≈ 2.8 hours. Real cards lose a bit to the filesystem, so expect ~93% of the theoretical number.
| Card | 1080p @ 24 Mbps | 4K @ 100 Mbps | 4K @ 150 Mbps |
|---|---|---|---|
| 64 GB | 5.9 h | 1.4 h | 57 min |
| 128 GB | 11.9 h | 2.8 h | 1.9 h |
| 256 GB | 23.7 h | 5.7 h | 3.8 h |
| 512 GB | 47.4 h | 11.4 h | 7.6 h |
Reading bitrates
Camera manufacturers rarely print the bitrate on the box. Common values: action cameras (GoPro/DJI) use 100–150 Mbps in 4K high mode, mirrorless cameras (Sony/Fuji/Panasonic) typically 50–200 Mbps depending on codec, iPhones record 35–50 Mbps in 4K, and dash cams are much leaner at 5–15 Mbps. If your camera has "bitrate" or "record setting" in the menu, use the real number.
Buying tips
- 4K at high bitrate eats cards fast: a week of daily 30-min vlogs at 150 Mbps needs ~236 GB — two 128 GB cards or one 256 GB card per week.
- Speed class matters for high bitrates: V30 (30 MB/s ≈ 240 Mbps) is enough for most 4K including 150 Mbps; choose V60/V90 only when your camera manual requires them (usually for very high bitrates or UHS-II cards).
- The reverse mode tells you what size to buy for a target recording time — useful before a trip where you can't offload.