How video file size works
Bitrate is how much data a video uses each second. Multiply it by the length and you have the file size. The resolution and frame rate don't appear in the formula directly; they affect how much bitrate you need for the video to look good.
The formula
video bitrate for a target = target size × 8 ÷ seconds − audio bitrate
Example: 10 minutes at 8 Mbps
| Step | Result |
|---|---|
| Total bitrate: 8 Mbps + 0.16 Mbps | 8.16 Mbps |
| Bits: 8.16 × 10⁶ × 600 s | 4.896 billion |
| Bytes: ÷ 8 | 612 MB |
Typical bitrates (H.264)
| Use | Resolution / FPS | Typical video bitrate |
|---|---|---|
| Live stream | 720p60 | 4–5 Mbps |
| Live stream | 1080p60 | 6–8 Mbps |
| Upload / export | 1080p30 | 8–12 Mbps |
| Upload / export | 4K30 | 35–45 Mbps |
| Local gameplay recording | 1080p60 | 20–50 Mbps |
| Local gameplay recording | 4K60 | 50–100+ Mbps |
Newer codecs like H.265 (HEVC) and AV1 reach similar quality at roughly 30 to 50% lower bitrates.
Frequently asked questions
How do you calculate video file size?
Add the video and audio bitrates, multiply by the length in seconds and divide by 8 to turn bits into bytes. 10 minutes at 8 Mbps video plus 160 kbps audio is (8 + 0.16) × 600 ÷ 8 = 612 MB.
What bitrate should I record gameplay at?
For local recordings in OBS with a hardware encoder, about 20 to 50 Mbps for 1080p60 and 50 to 100 Mbps or more for 4K60 keeps quality high for editing. Files get big fast, so many people use quality-based modes (CQP/CRF) instead of a fixed bitrate.
What bitrate should I stream at?
Twitch's general guidance for 1080p60 is around 6,000 kbps, and YouTube recommends higher bitrates for 1440p and 4K. Your upload speed should be comfortably above the stream bitrate, ideally with 25 to 50% to spare.
How do I fit a video under a file size limit?
Use the target size mode: it divides the size in bits by the duration and subtracts the audio bitrate. Encode at that video bitrate (or a little under, to leave room for the container) with two-pass encoding for the best quality.
Why is my file a bit bigger than calculated?
Container overhead (MP4, MKV) adds about 1 to 2%, and variable bitrate encodes can overshoot their average. Aim about 3 to 5% under a hard limit.
Rates and figures last checked October 2026.
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