Phone videos are big: a minute of 4K footage can be 300–400 MB. Email, chat apps and upload forms all have limits, and they change from time to time. Rather than memorise them, it helps to know how video size works so you can hit any limit quickly.
Typical limits (check before you send)
At the time of writing, these are the limits people most often run into. Services change them, so treat this as a guide and check the service’s help page if a file is close to the line.
- Email attachments: Gmail allows 25 MB in total per message and Outlook.com about 20 MB; larger files are sent as cloud links.
- Discord: free accounts have a 10 MB upload limit; paid plans allow more.
- WhatsApp: videos sent normally are compressed by the app; sending the file as a document keeps the original, up to 2 GB.
- Exam and job portals: often 2–20 MB, and usually MP4 only.
The one formula that matters
Video size is bit rate multiplied by duration. In practical units:
size in MB ≈ (video kbps + audio kbps) × seconds ÷ 8,000
A 60-second clip at 2,000 kbps video and 128 kbps audio is about 16 MB. To fit a limit, rearrange it: bit rate ≈ limit in MB × 8,000 ÷ seconds, minus the audio. For a 10 MB limit and a 45-second clip that is about 1,780 kbps total, so roughly 1,650 kbps for video. Our bit-rate calculator does this for you.
The fastest ways to shrink a video
- Trim it. Halving the duration halves the size with no quality loss. Trim video can cut without re-encoding.
- Lower the resolution. 4K to 1080p, or 1080p to 720p, lets the same bit rate look much sharper.
- Compress to a target size. Compress video takes a size in MB and works out the bit rate.
- Drop or reduce audio. Screen recordings often don’t need sound; speech is clear at 64 kbps.
How low can you go?
As a rule of thumb for H.264 MP4: 720p looks good from about 1,500–2,500 kbps, and 1080p from about 3,000–5,000 kbps. Below roughly 500 kbps, fast motion breaks into blocks. If the maths says you need less than that, trim the clip or lower the resolution rather than forcing the bit rate down.
Format matters too
MP4 with H.264 video and AAC audio plays everywhere: phones, Windows, Mac, smart TVs and every upload form that accepts video. iPhone videos are often HEVC in a MOV file, which some PCs and portals refuse. Converting MOV to MP4 fixes that, and you can compress in the same step.
Sources: Gmail Help, attachment size limits; Discord Support, file upload limits; WhatsApp Help Center.