Video Bitrate & File Size
File size from bitrate and duration, the bitrate that fits a target size, or how long a card or disk records — video plus audio, GB and GiB both shown.
The size of a recording or encode, the video bitrate a size budget allows after audio, the recording time a capacity gives, and the bytes per hour at that rate.
Example: 2 hours at 8 Mbps with 128 kbps audio is 7.32 GB (6.81 GiB); a 128 GB card records 35 h at that rate.
Bitrate times seconds,
over eight.
The one multiplication behind file size, the audio and overhead terms people forget, the GB-versus-GiB gap, and what variable bitrate does to the answer.
The arithmetic
Bytes = (video bit/s + audio bit/s) × seconds × (1 + overhead) ÷ 8. Two hours at 8 Mbps with 128 kbps audio is 8.128 Mbit/s × 7,200 s ÷ 8 = 7.32 GB. The other two questions solve the same equation for the bitrate a target size allows (after subtracting audio) and the recording time a capacity gives.
Units
Bitrates use decimal prefixes: 1 Mbps = 1,000,000 bit/s, as cameras, encoders and streaming platforms quote them. File sizes are shown in decimal GB and binary GiB (2³⁰ bytes) because a card is sold in the first and a file manager shows the second — a 7.32 GB file lists as 6.81 GiB.
Variable bitrate and overhead
A VBR encode with a target average lands near that average over the whole file, with peaks above and quiet scenes below; constant-quality modes (CRF) do not target a rate at all and the size is only known afterwards. Container muxing overhead (MP4, MKV, MOV headers and indexes) is usually under 2 % and is the figure you enter — none assumed.
What the number does not settle
Which bitrate a resolution and codec need for a given quality is a judgement the page does not make; the number here is size for a rate you already chose. Download & Transfer Time moves the file; Aspect Ratio & Pixels handles the frame. Inputs stay in your browser; the same four anonymous usage counts as the rest of the site apply.
SOURCES
Last reviewed 18 September 2026. How results are checked: How we verify.