How to Reduce Video File Size for Email or Chat
A video's size is roughly its bitrate multiplied by its length. Once you see that, you can work out in advance whether a clip will fit under an upload limit, and which setting to change.
The one formula that matters
Size in megabytes is roughly: total bitrate in kilobits per second × duration in seconds ÷ 8,000. For example, a 60-second clip at 480 kbps video plus 96 kbps audio (576 kbps) is about 576 × 60 ÷ 8,000 = 4.3 MB, plus a little container overhead. The same settings on a 5-minute clip give about 21 MB. Long videos need a lower bitrate, or trimming, to fit a fixed limit.
Levers, from most to least effective
- Trim what you do not need: half the length is half the size.
- Lower the resolution: 1080p to 720p lets a lower bitrate still look clean.
- Choose a lower bitrate or a higher CRF value (constant quality; higher means smaller).
- Lower the audio bitrate: 96 kbps AAC is fine for speech.
Size target or quality target?
If a service has a hard limit, use a fixed bitrate and do the arithmetic above. ToolkitPoint's Video Compressor has presets for email and messaging apps, but a fixed bitrate cannot promise a size for every length, so check the result. If you just want a smaller file that still looks good, use a CRF mode: 22 keeps high quality, 26 is balanced, and 32 compresses hard. Output is MP4 with H.264, which plays almost everywhere.
Why it is slow in a browser
Encoding runs as WebAssembly in your tab, so a minute of 1080p video can take several minutes on a typical laptop. Your video is not uploaded. Downscaling to 720p first makes it much faster. Upload limits change often, so check the service's current limit before choosing a target.
Primary sources and further reading
Last reviewed: September 28, 2026