How Video File Size Is Calculated
Video file size is determined primarily by the bitrate and duration. The formula is straightforward: File Size = (Video Bitrate + Audio Bitrate) × Duration / 8. The bitrate is measured in bits per second, so dividing by 8 converts to bytes. The total includes both the video stream and the audio track.
Bitrate is the single most important factor in file size. A higher bitrate means more data per second of video, resulting in higher quality but larger files. The codec determines how efficiently that data is compressed. Modern codecs like H.265 and AV1 achieve similar quality to H.264 at roughly half the bitrate.
Video Bitrate Guidelines by Resolution
For standard H.264 encoding: 720p typically uses 5-10 Mbps, 1080p uses 10-20 Mbps, 4K uses 35-68 Mbps, and 8K uses 80-160 Mbps. For H.265/HEVC, these values can be reduced by approximately 35-50% while maintaining similar visual quality. ProRes and RAW codecs use significantly higher bitrates as they prioritize editing flexibility over compression efficiency.
Codec Comparison
H.264 (AVC) is the most widely compatible codec, supported by virtually all devices. H.265 (HEVC) offers about 35% better compression than H.264. AV1 offers about 45% better compression and is royalty-free. ProRes 422 and 4444 are Apple's professional editing codecs with high bitrates but fast decoding. VP9 is Google's open-source codec used extensively on YouTube.
Frequently Asked Questions
How do I estimate video file size?
Multiply the total bitrate by the duration in seconds, then divide by 8 to convert bits to bytes.
What bitrate should I use for 4K video?
For 4K video, use 35-68 Mbps for H.264 or 15-35 Mbps for H.265/HEVC.
How much storage does 1 hour of 4K video use?
At 50 Mbps, one hour of 4K video uses approximately 22.5 GB.
Which codec produces the smallest files?
AV1 produces the smallest files for a given quality, followed by H.265/HEVC, then H.264.
Does frame rate affect file size?
Higher frame rates require higher bitrates for equivalent quality, resulting in larger files.