Bitrate, not resolution alone, determines file size. 4K at 100 Mbps fills storage about four times faster than 25 Mbps.
How to use the Video File Size Calculator
- Bitrate
- Duration
- Card or drive size
- Want to work backwards? Type a value into File size and Duration is calculated for you.
Results update as you type, and every field accepts the units shown in its menu.
How it works
Multiply the total bitrate (video plus audio) by duration in seconds and divide by 8 to get bytes.
Inputs explained
| Field | What to enter |
|---|---|
| Bitrate | Units: Mbit/s, kbit/s, Gbit/s |
| Duration | Units: min, s, h |
| Card or drive size | Units: GB, TB |
What each result means
- File size = [Bitrate]×[Duration]÷8
- Recording time on card = [Card or drive size]×8÷[Bitrate]
Example values
How the main result changes when Duration changes and everything else stays at the example values above:
| Duration (min) | File size (MB) |
|---|---|
| 5 | 1,875 |
| 7.5 | 2,812.5 |
| 10 | 3,750 |
| 12.5 | 4,687.5 |
| 15 | 5,625 |
| 20 | 7,500 |
Formula
File size = bitrate × duration ÷ 8Worked example
Inputs — Bitrate: 50 Mbit/s; Duration: 10 min; Card or drive size: 128 GB.
Results — File size = 3,750 MB; Recording time on card = 5:41:20.
Frequently asked questions
What bitrate does YouTube recommend for 4K?
About 35–68 Mbps for 4K at 24–60 fps (SDR).
Why is my file smaller than predicted?
Variable bitrate encoders use less data for simple scenes.
What formula does the Video File Size Calculator use?
File size = bitrate × duration ÷ 8.
Can I work backwards from the result?
Yes. Type the result you want into File size and the calculator finds the matching duration.