On the wire
—
Free tool
Will your PDF send, or bounce?
Email attachments grow ~37% in transit, so a file under the limit can still bounce. Enter your PDF size, pick where you're sending it, and see whether it fits — and exactly how far to compress if it doesn't.
Your file
Email limits include Base64 encoding overhead (~1.37×). Messaging apps upload the raw file.
Nothing is uploaded — the math runs in your browser.
Verdict
Checking…
Enter a size and pick a service.
Limit
—
Max raw PDF
—
Compress it on your phone.
PDF Toolkit shrinks oversized PDFs on-device — your contracts and statements never leave your iPhone. Free to start, no ads, no weekly subscription.
Reference
2026 attachment size limits
Gmail — 25 MB
Total message size; over the limit, Gmail swaps in a Google Drive link.
Outlook.com — 20 MB
Free Outlook.com caps at 20 MB; larger files go via OneDrive.
iCloud Mail — 20 MB
Standard limit is 20 MB; Mail Drop can send up to 5 GB via a 30-day iCloud link.
Yahoo Mail — 25 MB
25 MB per message, encoding included.
WhatsApp (document) — 2 GB
Up to 2 GB when sent as a Document — not via the photo picker, which crushes quality.
Slack (free) — 1 GB
Free workspaces allow up to 1 GB per file.
Discord (free) — 10 MB
Free users: 10 MB. Nitro Basic is 50 MB; full Nitro is 500 MB.
FAQ
How the check works
Why does my 24 MB PDF bounce from a 25 MB Gmail limit?
Email attachments are Base64-encoded for transport, which inflates them by roughly 37%. A 24 MB file becomes about 33 MB on the wire, over Gmail’s 25 MB message cap. For email services this checker applies that 1.37× overhead, so the largest raw PDF that reliably fits Gmail or Yahoo is about 18 MB, and about 14.5 MB for Outlook.com and iCloud Mail.
What are the current attachment limits?
As of 2026: Gmail and Yahoo 25 MB; Outlook.com and iCloud Mail 20 MB (iCloud Mail Drop handles up to 5 GB via a link); WhatsApp 2 GB for documents; Slack free 1 GB per file; Discord free 10 MB (50 MB Nitro Basic, 500 MB full Nitro). Email limits include encoding overhead; messaging apps upload the raw file, so this tool does not add overhead for them.
How small does my PDF need to be?
Pick your service above and the tool shows the largest raw PDF that fits and, if yours is too big, the target size to compress to. A safe universal target is under 10 MB, which clears every common email limit even after encoding.
Does this tool upload my PDF?
No. You type the file size in megabytes and it does simple arithmetic in your browser — nothing is uploaded or collected. To actually shrink the file on your iPhone, PDF Toolkit compresses on-device, so contracts and statements never leave your phone.
Need the full walkthrough? Read how to compress a PDF on iPhone or how to edit a PDF on iPhone.