How is video file size calculated?

Size in bits equals the total bitrate (video plus audio, in kbps) times 1000 times the duration in seconds. Divide by 8 for bytes. This tool does that and shows the result in B, KB, MB, GB or TB.

Why is my real file slightly different?

Variable-bitrate (VBR) encoding, container overhead and metadata mean the actual file can be a little larger or smaller. The estimate assumes a constant total bitrate.

No. The calculation runs entirely in your browser and nothing is sent anywhere.

Video File Size Calculator

Estimate a video file's size from duration and bitrate.

Video file size calculator

Estimate how big a video file will be from its duration and its video + audio bitrate. Useful for planning storage, picking an encoding target, or checking whether a clip will fit an upload limit.

The math is simple: total bitrate (kbps) × 1000 × seconds ÷ 8 = bytes. Enter your numbers and the size updates instantly — everything stays in your browser.