Video File Size from Bitrate Calculator

Understanding the video file size from bitrate calculator — concept and principle

This calculator predicts how large an encoded video file will be from its video bitrate, audio bitrate and running time. It is useful before you export or record: to check whether a clip fits an upload limit, a memory card or a USB stick, and to pick an encoder bitrate that hits a target file size.

Add the video and audio rates, multiply by seconds, divide by 8 for bytes.

How it is calculated

File size (MB) = (video bitrate in Mbps × 1,000,000 + audio bitrate in kbps × 1,000) × minutes × 60 ÷ 8 ÷ 1,000,000

The GB result is the same number divided by 1,000,000,000 instead of 1,000,000. Video bitrate is entered in megabits per second, audio in kilobits per second, and duration in minutes. Both bitrates are first converted to bits per second and added, multiplied by the duration in seconds to get total bits, then divided by 8 to get bytes. Units are decimal: 1 MB = 10^6 bytes.

The principle

A bitrate is literally "bits per second", so a stream of known rate carries rate × time bits. The video and audio tracks are stored side by side in the same file, so their rates add. For constant bitrate (CBR) encodes the prediction is very close; for variable bitrate (VBR) encodes, enter the average bitrate, because simple scenes use fewer bits and complex scenes more, and the file size follows the average. The container (MP4, MKV, MOV) adds only a little indexing and metadata.

Worked example

Inputs: video 8 Mbps, audio 192 kbps, duration 10 minutes.
Total bitrate: 8,000,000 + 192,000 = 8,192,000 bit/s.
Duration: 10 × 60 = 600 s.
Total bits: 8,192,000 × 600 = 4,915,200,000 bits.
Bytes: 4,915,200,000 ÷ 8 = 614,400,000 bytes = 614.4 MB, or 0.6144 GB.

Each point is the calculator re-run with only “Duration (min)” changed; the gold point is the default example. Change the inputs above and this chart follows your numbers.

Duration (min)	File size (MB)
2.5	153.6
5	307.2
7.5	460.8
10	614.4
12.5	768
15	921.6
20	1,228.8

How to read the result

Use the result as a planning figure. To reverse the calculation and hit a size limit, rearrange: total bitrate (bit/s) = size in bytes × 8 ÷ seconds, then subtract the audio rate to get the video budget. Bitrates commonly used for H.264 web uploads are roughly 5–8 Mbps for 1080p at 30 fps and higher for 4K; efficient codecs such as HEVC or AV1 reach similar quality at lower rates. If the file comes out larger than predicted, the encoder probably exceeded its average or the audio rate was higher than assumed.

Common mistakes

Confusing megabits (Mb) with megabytes (MB); one byte is eight bits.
Entering the peak (maximum) VBR rate instead of the average.
Forgetting the audio track, which matters for low-bitrate video.
Comparing the decimal result with a file manager that shows binary MiB or GiB.

Keep in mind: The estimate covers audio and video payload only. Container overhead, subtitle or extra audio tracks and encoder rate-control variation make real files slightly different, so leave a margin of a few percent when a hard limit applies.

Frequently asked questions

How do I find the bitrate needed for a 2 GB, 60-minute video?

2,000,000,000 × 8 ÷ 3,600 is about 4.44 Mbps in total; subtract the audio (for example 0.128 Mbps) to get about 4.3 Mbps for video.

Why does my file manager show a smaller number?

Windows reports sizes in binary units. 614.4 MB is about 585.9 MiB, though it may be labelled "MB".

Sources: ISO/IEC 14496-12, ISO base media file format (MP4 container) · ITU-T Recommendation H.264, Advanced video coding for generic audiovisual services

Checked 8 Nov 2026. Standard formulas and RFC/IEEE definitions, computed locally in your browser — nothing you type is sent anywhere.

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