Know your limit first
Every email provider caps the total size of a message, attachments included. As of October 2026, the main limits are:
| Provider | Message limit | Safe PDF size |
|---|---|---|
| Gmail | 25 MB (Google Help) | about 18 MB |
| Outlook.com | 20 MB | about 14 MB |
| Yahoo Mail | 25 MB | about 18 MB |
| Many company mail servers | 10 MB is common | about 7 MB |
Why is the "safe" size so much lower? Email was built for text. Attachments are converted to base64 before they're sent, and base64 turns every 3 bytes into 4 characters, so the attachment grows by about 33%. A 20 MB PDF arrives at the mail server as roughly 26.7 MB, which is over Gmail's limit. Divide the limit by 1.37 or so to leave room for the encoding and the email itself. That's where the third column comes from.
The recipient's server has a limit too. If you're sending to a company or a government office, 10 MB is a sensible ceiling even when your own provider allows more.
Step by step: compress the PDF
- Open Compress PDF and drop in your file. It's processed in your browser, so a contract or bank statement isn't uploaded anywhere.
- Choose Lossless clean-up first. It rebuilds the file more compactly: it removes objects nothing points to, compresses streams that were stored uncompressed and recompresses the rest at maximum level. Text, links and form fields stay exactly as they were.
- Tick Remove metadata if you don't need the title, author, XMP data and embedded page thumbnails. Files exported from design apps can carry large chunks of private editor data, and this removes it.
- If the file is full of photos, tick Also shrink JPEG photos. Only those photos are re-encoded, and only when that saves at least 5%. Text and drawings aren't touched.
- Check the result. If it's under your safe size, you're done. If it isn't, go to the next section.
When lossless isn't enough: scans and photo-heavy PDFs
A scanned document is already a stack of images, so a lossless clean-up can't shrink it much. That's when you need Strong mode. It renders every page as a JPEG and builds a new PDF from those images. The trade-off is real: text stops being selectable and searchable, and links, bookmarks and form fields are lost. That's usually fine for a scan, which had no real text to begin with. It's a bad idea for a digital contract you'll need to search later.
The resolution you choose decides most of the final size. Here's how many pixels one US Letter page (8.5 × 11 in) becomes at each setting:
| Resolution | Pixels per page | Megapixels | Good for |
|---|---|---|---|
| 72 dpi | 612 × 792 | 0.48 | On-screen reading only |
| 100 dpi | 850 × 1,100 | 0.94 | Screen, and printing if the text is large |
| 150 dpi | 1,275 × 1,650 | 2.10 | Printing with small print still readable |
Going from 150 dpi to 100 dpi cuts the pixel count by more than half (2.10 to 0.94 megapixels), and the file shrinks by a similar amount. Going down to 72 dpi halves it again. For a 40-page scan that has to go to Gmail, start at 150 dpi. Drop to 100 dpi only if the result is still over about 18 MB.
A worked example
Say you have a 40-page scanned lease at 31 MB, and Gmail is your target. Lossless clean-up might only take it down to 29 MB, since the content is all images. Strong mode at 150 dpi gives each page about 2.1 megapixels. At typical JPEG quality, that's often a few hundred kilobytes per page, so the whole lease lands in the 8–15 MB range. That's under the safe 18 MB. Your exact numbers will vary with how busy the pages are. The tool shows the before and after sizes, and it offers you the original back if the "compressed" file turns out bigger.
Other ways to make a PDF smaller
- Delete pages nobody needs. Blank scanned backs, cover sheets and duplicate pages all cost space. Remove them in the PDF Page Organizer before you compress.
- Re-export from the source. If you made the PDF from Word or a design app, re-export it with a "smaller file" or "minimum size" preset. This usually beats compressing afterward.
- Scan at a sensible setting. 200–300 dpi grayscale is plenty for text documents. Scanning at 600 dpi in color makes files that are many times larger with no visible benefit.
- Split it. If it still won't fit, use Merge & Split PDF to cut it into ranges like
1-20, 21-and send two emails.
When to send a link instead
Gmail offers to send files over 25 MB as a Google Drive link, and Outlook.com does the same with OneDrive. Links get around the size limit completely. But the recipient needs access permissions set correctly, some organizations block cloud links, and a link can stop working later. For legal or official submissions that ask for an attachment, compress or split the file instead.
Quick checklist
- Find the smallest limit between you and the recipient, and multiply it by about 0.73.
- Delete unneeded pages.
- Run lossless clean-up with metadata removal and JPEG shrinking turned on.
- For scans only, use Strong mode at 150 dpi, then 100 dpi if needed.
- Still too big? Split the file into parts.
Combining files before you send them? See how to combine PDF files into one, and compress the merged file last.