Video file size and bitrate calculator

Size = bitrate × time

A video's bitrate is how many bits it uses for each second of footage. Multiply by the running time and divide by 8 for bytes. 8 Mbps for an hour: 8,000,000 × 3,600 ÷ 8 = 3,600,000,000 bytes, 3.6 GB. Add the audio track the same way: 128 kbps for an hour is 57.6 MB.

Working backwards gives the bitrate you can afford: bits available ÷ seconds. That is how you fit a film onto a disc or a clip under an upload limit. Subtract the audio before you set the video bitrate.

Resolution doesn't set the size; it sets the bitrate you need to look good. The presets use YouTube's published upload recommendations for H.264 (8 Mbps for 1080p30, 35–45 Mbps for 4K30). HEVC and AV1 typically need about 40–50 % less bitrate than H.264 for similar quality. These factors are rules of thumb (estimates); real savings depend on the encoder and the footage.

Most cameras and phones record at a variable bitrate, so real files differ from the arithmetic by a few percent either way.