What this calculator does
Video file size is driven almost entirely by two numbers: the bitrate, which is how much data is recorded for each second of footage, and the duration of the footage itself. Multiplying the two together, then converting from bits to bytes, gives the resulting file size.
This is the calculation behind working out how much footage will fit on a memory card or drive, or how large a finished export will be before uploading or sharing it. Higher bitrates capture more detail and handle motion and compression artefacts better, at the direct cost of a larger file for the same length of footage.
The formula
Multiply the bitrate in megabits per second by the duration in seconds, then divide by 8 to convert from megabits to megabytes, since there are 8 bits in a byte. Dividing the result by 1024 gives the equivalent file size in gigabytes for longer footage.
| Term | Meaning |
|---|---|
| Bitrate | The amount of video data recorded per second, in megabits per second (Mbps). |
| File size (MB) | (bitrate × duration in seconds) ÷ 8. |
| File size (GB) | The megabyte figure divided by 1024, more convenient for longer recordings. |
The inputs explained
| Field | What to enter |
|---|---|
| Bitrate (Mbps) (Mbps) | The recording bitrate in megabits per second, as set in the camera or export settings. |
| Duration (minutes) | The whole minutes of footage duration. |
| Duration, extra seconds | Any extra seconds beyond the whole minutes entered above. |
When to use it
Planning memory card capacity
Knowing the file size per minute at a given bitrate lets you work out how much footage a card of known capacity will actually hold before a shoot.
Comparing recording settings
Different bitrate or codec settings produce very different file sizes for the same length of footage, and comparing them helps balance quality against storage and backup cost.
Estimating export or upload size
Before exporting a finished video at a chosen bitrate, estimating the resulting file size helps judge upload time or whether it fits a platform’s file size limit.
Worked examples
Every figure in the tables below is produced by this page’s own calculator at build time, so the numbers and the tool always agree. Select any row to load that scenario.
How file size changes with bitrate at a fixed duration
A fixed 10-minute clip, across a range of recording bitrates.
| Bitrate | File size | File size (GB) |
|---|---|---|
| 25 Mbps | 1,875 MB | 1.83 GB |
| 50 Mbps | 3,750 MB | 3.66 GB |
| 100 Mbps | 7,500 MB | 7.32 GB |
| 150 Mbps | 11,250 MB | 10.99 GB |
| 200 Mbps | 15,000 MB | 14.65 GB |
| 400 Mbps | 30,000 MB | 29.30 GB |
How file size changes with duration at a fixed bitrate
A fixed 100 Mbps bitrate, across a range of clip durations.
| Duration | File size | File size (GB) |
|---|---|---|
| 1 min | 750 MB | 0.73 GB |
| 5 min | 3,750 MB | 3.66 GB |
| 10 min | 7,500 MB | 7.32 GB |
| 20 min | 15,000 MB | 14.65 GB |
| 30 min | 22,500 MB | 21.97 GB |
| 60 min | 45,000 MB | 43.95 GB |
Questions
Does resolution affect this calculation directly?
Not directly. Resolution, frame rate and codec efficiency all influence what bitrate is needed for a given quality level, but once the bitrate is known, file size follows from bitrate and duration alone regardless of what resolution produced that bitrate.
Why is my actual file slightly different from the estimate?
Most cameras and encoders use a variable bitrate that fluctuates around a target average depending on scene complexity, so the actual file size is usually close to but not exactly the calculated figure, plus a small amount of container and audio overhead.
Why divide by 8 in the formula?
Bitrate is conventionally measured in megabits per second, but file sizes are reported in megabytes, and there are 8 bits in a byte. Dividing by 8 converts the total data from megabits to megabytes.
How much does audio add to the file size?
Audio tracks typically add a relatively small amount compared with video at normal bitrates, often in the range of a few hundred kilobits per second, but this calculator covers only the video bitrate entered, so add audio separately if a precise total is needed.
To estimate the total storage a full shoot of photos and video will need, see the photo shoot storage calculator.