About this tool
Video Bitrate & File Size Calculator is a free, in-browser tool that solves any one of file size, bitrate or record time from the other two, plus an optional audio track. Nothing is uploaded — the math runs locally as you type.
The core relationship is file size (MB) = bitrate (Mbps) × duration (s) ÷ 8, since eight bits make a byte. Rearranged, bitrate = size × 8 ÷ duration and duration = size × 8 ÷ bitrate. Any audio bitrate you enter (in kbps) is converted to Mbps and added to the video bitrate before the size or time is worked out. For reference, 1080p30 H.264 is roughly 8–12 Mbps and 4K30 around 35–45 Mbps.
Use it to check whether a shoot fits a card, to hit a target upload size, or to see how long a card records at a given bitrate before you press record.
Frequently asked questions
How is video file size calculated?
File size in megabytes = bitrate in Mbps × duration in seconds ÷ 8. The ÷ 8 converts megabits to megabytes. A 10 Mbps clip for 60 seconds is 10 × 60 ÷ 8 = 75 MB.
What bitrate do common resolutions use?
As a rough H.264 guide: 720p30 ≈ 5 Mbps, 1080p30 ≈ 8–12 Mbps, 1080p60 ≈ 12–18 Mbps, 4K30 ≈ 35–45 Mbps and 4K60 ≈ 50–70 Mbps. Efficient codecs like H.265/HEVC and AV1 reach similar quality at roughly half those numbers.
How does the audio bitrate factor in?
Audio is entered in kbps, converted to Mbps and added to the video bitrate before computing size or record time. Typical audio is 128–320 kbps for stereo AAC, so it adds only a small amount to most files.
Is anything uploaded?
No. You enter numbers and the result is computed in your browser. No video or data is uploaded, and it works offline.
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