Bitrate Calculator (Video File Size)
Find the video bitrate that hits a target file size for a 2-pass encode, or the file size of a given bitrate and duration, with audio and container overhead included.
Two-pass encoding hits the average bitrate closely; one-pass CRF encodes cannot target a size. Rounding down keeps the file just under the limit.
| Target size | Video kbps |
|---|---|
| 10 MB | 5 |
| 25 MB | 205 |
| 50 MB | 538 |
| 100 MB | 1,205 |
| 250 MB | 3,205 |
| 500 MB | 6,538 |
| 1 GB | 13,205 |
| 2 GB | 26,538 |
| 4 GB | 53,205 |
File size is bitrate multiplied by time. When a video must fit an upload limit, this calculator gives the video bitrate to use for a two-pass encode after subtracting the audio, plus a ready ffmpeg command; in the other direction it tells you how big a recording or export at a given bitrate will be. Decimal (MB, GB) and binary (MiB, GiB) sizes are both supported.
How to use this tool
- Choose whether you know the target size or the bitrate.
- Enter the duration in hours, minutes and seconds.
- Enter the target size (or the video bitrate) and the audio bitrate and number of tracks.
- Add container overhead if you want a safety margin, then copy the bitrate or ffmpeg command.
Formula
total kbps = size in bytes × 8 ÷ seconds ÷ 1000 ÷ (1 + overhead) · video kbps = total − audio kbps × tracks · size = (video + audio) × 1000 × seconds ÷ 8
Bitrates are in kilobits per second (1 kbps = 1,000 bits/s). 1 MB = 10⁶ bytes; 1 MiB = 1,048,576 bytes. Container overhead (headers, indexes) is small, usually under 2% for MP4 and MKV.
Example
To fit a 10-minute clip into 100 MB with 128 kbps audio: 100,000,000 × 8 ÷ 600 s = 1,333.3 kbps in total, so the video gets 1,205 kbps. In reverse, 5,000 kbps for 60 seconds is 5,000 × 1,000 × 60 ÷ 8 = 37,500,000 bytes = 37.5 MB.
Frequently asked questions
Why is my file slightly larger than the target?
Encoders hit the average bitrate only approximately, and containers add a little overhead. Set 1–2% overhead or round the bitrate down for a hard limit.
What bitrate looks good?
It depends on resolution, frame rate, codec and motion. As a rough guide, H.264 1080p30 looks clean around 5–8 Mbps; HEVC and AV1 need noticeably less for the same quality.
Should I use CRF or two-pass?
CRF gives constant quality with an unpredictable size; two-pass with a target bitrate gives a predictable size. Use two-pass when a size limit matters.
Last updated:
Page address with these inputs: https://kakao.mobile/tools/bitrate-calculator/
Cite or embed this tool
kakaoCalc. (2026, November 8). Bitrate Calculator (Video File Size). https://kakao.mobile/tools/bitrate-calculator/
“Bitrate Calculator (Video File Size).” kakaoCalc, 8 Nov. 2026, kakao.mobile/tools/bitrate-calculator/.
Paste this code into your page. The widget runs in your visitors' browsers, shows no ads and keeps a link back to this page. Embedding terms