Make a PDF Under 25MB (Gmail)
Gmail allows 25 MB attachments, but you may need a smaller target to avoid encoding overhead. Use these steps to fit your PDF under 25 MB.
Step 1: Choose the Gmail 25 MB preset
Select the Gmail preset to target 25 MB and let PDFThin optimize the file without visible changes.
If the file is scan-heavy, expect additional optimization or splitting.
Step 2: Drop to 20 MB when needed
If the attachment still fails to send, use a custom target between 18-20 MB.
This smaller target accounts for Base64/MIME overhead and improves delivery success.
Step 3: Split if a single file cannot fit
When compression cannot reach 25 MB, use Split by size to get multiple parts under the limit. Attach the parts in order to keep the document flow intact.Step 4: Verify before sending
Check the final file size before attaching. This prevents last-minute errors in Gmail.
If you see warnings, lower the target by a few MB and retry.
FAQ
Does Gmail compress my PDF?
No. Gmail does not compress PDF attachments. You must compress before uploading.
Why does a 25 MB file fail?
Encoding overhead can push the message over the limit. Use 18-20 MB for reliability.
Is splitting better than compression?
Compression keeps a single file when possible. Split only when needed to meet the limit.
Gmail best practices
Leave headroom
Aim slightly below 25 MB to prevent send errors, especially with multiple attachments.
A 20 MB target works well across Gmail and Outlook.
Keep parts readable
If you split, verify that each part opens correctly and retains page order.
This ensures the recipient can review the document without confusion.
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