Why is my video too big to email when it is under 25 MB?

What counts toward the limit

• Google says its Workspace sending limits are "the limits on the total size of the message content and attachments before encoding". So the text of the email counts, not only the video.
• Microsoft says the Outlook limit "includes both the size of the attachment and the size of the email".
• Yahoo says the sum of all attached files in a single message, for both incoming and outgoing email, must not exceed 25 MB.
• For personal Gmail accounts, Google says that if your total attachment size is greater than the limit, Gmail automatically removes the attachment and adds it as a Google Drive link in the email.

Why encoding makes the video bigger

• Email carries a video as printable characters. RFC 2045 says base64 turns each 24-bit group of input into 4 encoded characters, and that the encoded data are "consistently only about 33 percent larger than the unencoded data".
• The same RFC says encoded lines must be no longer than 76 characters, so the line breaks add a little more.
• Google says its Workspace sending limits are counted before encoding. Its page on Workspace receiving limits says those figures are "the limit after encoding, which adds about a 37% increase".

What we measured

We ran our two compression tools on a 30-second, 1080p test video of 48.3 MB that we generated ourselves. We then wrapped each result as an email attachment in the standard way, with base64, 76-character lines and CRLF line endings, using Python's email library. We measured the whole message on 2026-10-19.

• Compress video for email: a 17.17 MB file became a 23.50 MB message, 36.8% bigger.
• Compress video to 25 MB: a 23.36 MB file became a 31.97 MB message, 36.8% bigger.

The 36.8% matches the arithmetic. Three bytes become four characters, and each 76-character line gets a 2-byte line ending, so the size is multiplied by 4/3 and by 78/76, which is about 1.368. It also matches Google's "about 37%".

That is the reasoning behind the 18 MB target on our email page. 18 MB plus 36.8% is about 24.6 MB, which is still under 25 MB.

What we did not test

We did not send these files through Gmail, Outlook, Yahoo or any other mail service, so we cannot say how a particular service counts a message. The sources above say Google counts its Workspace sending limits before encoding and its Workspace receiving limits after. They do not say how Outlook or Yahoo count. We used one test video.

What you can do

1. Add up everything in the message: the video, any other attachments, and the text.
2. Leave room. At 36.8% extra, a 20 MB video is about 27.4 MB as a message, which is over 25 MB if the service counts after encoding.
3. Make a smaller copy with Compress video for email. It runs in your browser, and your video is not uploaded.
4. For Gmail's own limits, see the Gmail attachment guide.

More plain answers are in all guides.