How this calculator works
A codec records a stream of bits, and its bitrate states how many bits each second of video uses. Dividing by eight converts megabits to megabytes, and multiplying by the duration gives the file size, before a small allowance for the container and audio. Intra-frame formats such as ProRes and DNxHD encode every frame on its own at a nearly constant bitrate, so the estimate is close. Long-GOP formats such as H.264 and MPEG-2 vary their bitrate with scene complexity, so their files can differ by a large factor. The presets here are typical 1080p values at about 30 frames per second; recording 4K, higher frame rates or different raw settings changes them, so enter a custom bitrate when you know the camera specification.
Formula
file size (bytes) = bitrate (bit/s) x duration (s) / 8. size per minute = bitrate x 60 / 8. size per hour = bitrate x 3600 / 8. 1 Mbit/s is 1,000,000 bit/s.
Worked example
ProRes 422 at 1080 has a bitrate of about 147 Mbit/s. A one minute clip is 147,000,000 x 60 / 8 = 1,102,500,000 bytes, or 1.1025 gigabytes, and an hour is 66.15 gigabytes. DNxHD 145 for ten minutes gives 145,000,000 x 600 / 8 = 10.875 gigabytes. Uncompressed 1080 10-bit at 622 Mbit/s fills 777.5 megabytes in ten seconds.
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Frequently asked questions
Why do my camera files differ from the estimate?
The presets are typical rather than exact. Frame size, frame rate, chroma subsampling, audio and the codec settings all change the bitrate, and long-GOP codecs also vary with the scene. Use the camera specification for a custom figure.
Which formats are constant bitrate?
Intra-frame formats such as ProRes, DNxHD and uncompressed video are close to constant, which makes their size predictable. H.264, HEVC and MPEG-2 use variable bitrate, so their figures are averages.
Is audio included?
No. Add roughly 1.5 Mbit/s for 48 kHz 24-bit stereo uncompressed audio, or a few hundred kbit/s for compressed audio. For long recordings the audio can be a percent or two of the video size.
Why use gigabytes rather than gibibytes?
This calculator uses decimal units, where 1 GB is 1,000,000,000 bytes, which matches drive and card marketing. Operating systems often report binary units, so the same file shows a smaller number there.