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Outlook attachment too large? Shrink it under 20 MB

Microsoft's help page says the limit for internet accounts such as Outlook.com is 20 MB, and the default for Exchange work accounts is 10 MB. The limit counts the attachment and the email together.

  • Nothing is uploaded. Your browser does the compression, so the file stays on your device.
  • Lands under the real limit. We aim a little below it, so the upload goes through first time.
  • Fast. A 30 second 1080p clip fits into 10 MB in about two seconds on a desktop.
Where are you sending it?

Custom size 20.00 MB. We aim for 19.40 MB, a small safety margin so the file never lands just over.

Sent to our servers: 0 bytes. It all happens in this tab.

When you need 20.00 MB

If you use a work Outlook account, ask which limit applies. Many companies keep the 10 MB default, and then the 10 MB page is the safe choice.

What to expect

A 90 second 1080p clip typically lands at 480p to 540p within 20 MB. Shorter clips stay sharper.

How much video fits in 20 MB

Worked out with the same maths the compressor uses, for a typical 1080p phone or screen clip with sound. Fast motion needs more room, still scenes and screen recordings need less.

Clip lengthResolution we pickHow it looks
10 seconds1080pSharp
30 seconds1080pSharp
1 minute720pSharp
2 minutes540pGood on a phone
5 minutes360pWatchable, small
10 minutes270pWatchable, small

How we hit the number

We work out how many bits each second of video can use: the target size, minus a safety margin, divided by the length, minus the audio. Then we pick the largest resolution that still looks clean at that rate and encode with your browser's built-in video encoder. If the result is still over, we automatically try once more at a lower rate.

The target we aim for is 19.40 MB, which is 600 KB under 20.00 MB, so the file is not turned away over a few bytes.

Questions people ask

Is it 20 MB or 25 MB?

Microsoft's own support page says 20 MB for Outlook.com and similar accounts. Some third-party sites say 25 MB. Aiming for 20 MB works either way.

My work account still refuses a 15 MB file.

Exchange accounts often default to 10 MB. Use the 10 MB option, or ask your administrator.

Related

Limits change. We link the official page wherever there is one, and the safety margin means a small change is unlikely to matter. Last updated 2026-11-09.