File Size Calculator
Overrides the preset.
- 1125.0
- Size (MB, decimal)
- 1072.9
- Size (MiB, binary)
- 1.125
- Size (GB, decimal)
- 5 Mbps
- Bitrate used
The file size calculator estimates how large a video or audio file will be from its duration and bitrate, using seven realistic presets from 720p streaming to 4K ProRes. Results are shown in both decimal megabytes and binary mebibytes, because storage and operating systems disagree about which one MB means.
How it works
bytes = minutes x 60 x Mbps x 1,000,000 / 8
- x 60
- minutes to seconds
- / 8
- bits to bytes: bitrates are quoted in megabits, file sizes in megabytes
That division by eight is where most mental estimates go wrong. A 5 Mbps stream is 0.625 MB per second, not 5.
- The presets assume constant bitrate. Real encoders vary the rate with scene complexity, so a mixed-content video lands within about 15 percent of the estimate.
- ProRes 422 at 492 Mbps produces roughly 3.7 GB per minute, which is why editing formats need very different storage planning from delivery formats.
- Audio presets cover 320 kbps MP3 and uncompressed CD-quality WAV at 1.411 Mbps.
Examples
A half-hour of 1080p
Duration
30 minutes
Format
1080p H.264, streaming (5 Mbps)
Result
1,125.0 MB decimal · 1,072.9 MiB binary
30 × 60 × 5 × 1,000,000 / 8. The two figures describe the same file, only the definition of "mega" differs.
The same duration in ProRes
Duration
30 minutes
Format
4K ProRes 422 (492 Mbps)
Result
110,700 MB: about 110 GB
Nearly a hundred times larger than the streaming version. Editing codecs trade size for quality and decode speed.
An album in MP3
Duration
45 minutes
Format
Audio only, 320 kbps MP3
Result
108.0 MB
0.32 Mbps for 2,700 seconds. The same album as WAV would be 476 MB.
Frequently asked questions
Why is my actual file smaller or larger than the estimate?
Because real encoders use variable bitrate, spending more bits on complex scenes and fewer on simple ones. The quoted bitrate is an average target. A file of mixed content usually lands within about 15 percent; a video that is mostly static or mostly action can miss by considerably more.
Why are two different sizes shown?
Because MB is ambiguous. Decimal megabytes are 1,000,000 bytes and are what storage and streaming figures use; binary mebibytes are 1,048,576 bytes and are what most operating systems display while still labelling them MB. The gap is 4.9 percent at this scale.
What bitrate should I use for uploading?
Around 5 Mbps for 1080p and 15 for 4K covers most platforms, which then re-encode anyway. Uploading at a much higher bitrate mainly costs you time, the platform’s own encoder determines what viewers receive.
Does resolution or bitrate determine file size?
Bitrate alone. Resolution influences what bitrate looks acceptable, but a 4K file at 5 Mbps is exactly the same size as a 1080p file at 5 Mbps, it just looks considerably worse.