How to shrink a video enough to actually send it

"This file is too large to attach" is one of the few computer problems with an exact answer. You know the target, you know the length, and the arithmetic between them tells you what to set. Guessing at a quality slider is what makes this feel hard.

The limits, as of 2026

• Gmail, Outlook and most email — 25 MB per message. Attachments are Base64-encoded in transit, which inflates them by about a third, so aim for 18–20 MB of actual file to be safe.
• WhatsApp — 16 MB for a video sent as media, and it re-compresses what you send anyway. Sending as a document instead raises the limit to 2 GB and skips the re-compression entirely.
• Telegram — 2 GB, or 4 GB with Premium. Rarely the problem.
• Discord — 10 MB on a free account, 50 MB with Nitro Basic, 500 MB with full Nitro.
• Slack — 1 GB per file, but workspace storage is the real constraint on free plans.
• iMessage — around 100 MB, and it silently re-compresses heavily on cellular.

Work backwards from the limit

Rearrange the file-size formula and it tells you the bitrate to use:

total bitrate (kbps) = (target MB × 8,192) ÷ length in seconds

Then subtract the audio. 128 kbps is generous for anything with speech; 96 is fine.

A worked example. A 3-minute clip for a 20 MB email:

• (20 × 8,192) ÷ 180 = about 910 kbps total
• minus 128 kbps of audio leaves 780 kbps for video

780 kbps is not much. It is unusable at 1080p, perfectly acceptable at 480p, and fine at 720p if the footage is mostly static — a talking head or a screen recording. That single number has just told you the resolution to export at, without any trial and error.

What to change, in order

1. Trim it. Length is a straight multiplier on size and the easiest thing in the list. Almost every video that is too big has ten seconds of fumbling at the start and five at the end. Cutting a three-minute clip to two removes a third of the file for free, with no quality cost whatsoever. Our video trimmer cuts on keyframes without re-encoding where it can, so the trim itself is lossless and instant.

2. Drop the resolution to what the recipient will actually see. Someone opening this on a phone in a chat app is looking at a screen a few inches wide. 4K is pure waste there. 720p is more than enough, and 480p is genuinely fine for a quick clip. Use the video resizer for this.

3. Set the bitrate from the formula above. Not a "medium" preset — the actual number, worked out from your actual target. This is the step that makes the file the size you need rather than some size.

4. Halve the frame rate if the content allows. 60 fps to 30 fps saves a useful chunk. Fine for a talking head, a demo, a screen recording. Not fine for sport or fast panning.

5. Change codec last. H.265 at the same bitrate looks considerably better than H.264, so it lets you go lower. But not every device plays it, and a file the recipient cannot open is worse than one they cannot receive. For anything going to a stranger, stay on H.264.

Our video compressor does all of this in the browser with a real FFmpeg build, so nothing is uploaded and there is no queue — which also means a 500 MB source is limited by your machine's memory rather than by somebody's upload quota.

The alternative worth considering first

Sometimes the right answer is not to compress at all. Upload the original to Google Drive, Dropbox, OneDrive or WeTransfer and send a link. The recipient gets full quality, you skip the whole exercise, and for anything that matters — a wedding video, footage a client will edit — that is plainly the better outcome. Compression is for when a link is not appropriate or not possible.

Things that do not work

Zipping it. Video is already compressed; a ZIP saves a fraction of a per cent. This surprises people every time.

Renaming the extension. Changes nothing about the contents. An .mp4 renamed to .mov is an MP4 with a misleading name.

Splitting into parts. Technically works for email, but you are asking the recipient to reassemble archive volumes in 2026. Send a link.

Compressing an already-compressed export again. Each pass compounds the last one's artefacts. If the first attempt came out too big, go back to the original and compress that harder — do not compress the compressed one.

Quick reference

Total bitrate to hit a target, by clip length:

• 30 seconds into 20 MB → ~5,400 kbps. 1080p is comfortable.
• 1 minute into 20 MB → ~2,700 kbps. 1080p at moderate quality, or 720p comfortably.
• 3 minutes into 20 MB → ~910 kbps. 480p, or 720p for static content.
• 5 minutes into 20 MB → ~545 kbps. 480p and expect visible compression on motion.
• 10 minutes into 20 MB → ~270 kbps. Send a link instead.

That last row is the useful one. When the arithmetic tells you the answer is 270 kbps, the arithmetic is telling you not to attach the file — and it is better to know that in ten seconds than after four failed exports.