Gmail's documented cap is 25MB per message, covering the message body plus every attachment combined. That number is smaller in practice than it looks, because Gmail encodes attachments in base64 for transit, which adds roughly a third to a file's effective size against that budget.
Compress a PDF nowThe 25MB figure Gmail advertises is a post-encoding limit, not a limit on your raw file size — base64 encoding, which email uses to transmit binary attachments like PDFs as text, inflates the effective size of an attachment by roughly one-third. That means a 25MB message budget represents meaningfully less than 25MB of actual file content once encoding overhead is accounted for. On top of that, Gmail's own web client automatically converts an attachment that would exceed the limit into a Google Drive share link instead of a direct attachment, which is not always what a recipient expects or can open.
Because base64 encoding adds about a third to your file’s effective size in transit, a raw PDF needs real headroom below Gmail’s 25MB cap, not just to sit right at the edge of it.
Add the file in your browser — the tool compresses on-device, with no server upload needed before you attach the result to your Gmail message.
Recommended-quality compression gives real headroom under Gmail’s cap after encoding, and avoids triggering Gmail’s automatic conversion to a Drive link.
A properly compressed PDF can be sent as a normal attachment rather than a Drive share link, which some recipients cannot open without a Google account.
Gmail automatically switches to a Drive share link when an attachment (accounting for base64 encoding overhead) would push the message over its 25MB cap — compressing the PDF first, so it fits comfortably within that budget, keeps it as a normal attachment.
It applies per message, and covers the message body plus every attachment combined — if you are sending multiple files, their combined effective size (after encoding) is what counts against the cap.
Because encoding adds roughly a third to the effective size, aim well below the raw 25MB mark — Recommended-quality compression on anything sizable gives a comfortable safety margin rather than sitting right at the edge.