Email Attachment Size Checker
Check email attachment size limits for Gmail, Outlook, Yahoo, Apple Mail, and 12+ providers. Includes a file size calculator with Base64 encoding overhead, blocked file type reference, and tips for sending large files.
About this tool
Every email provider has different attachment size limits, and hitting them causes frustrating bounce-backs. Gmail caps at 25MB, Outlook at 20MB, and when you factor in Base64 encoding overhead (which adds ~37% to your file size), a 19MB file can already be too large for some providers.
This tool lets you check your file size against every major email provider's limits instantly. It accounts for Base64 encoding — the conversion that happens behind the scenes when you attach binary files to email — so you get an accurate picture of whether your attachment will make it through.
You'll also find a complete reference of which file types get blocked (executables, scripts, disk images), which are always safe (PDFs, images, documents), and why marketing emails should never include attachments in the first place.
If you're building email campaigns, our email word counter helps you make sure the total email (HTML + images) stays under clipping thresholds. For signature images, check our signature size guide, and for campaign header images, see our email banner size guide. Our deliverability score tool can help you check if attachments are affecting your sender reputation.
Frequently Asked Questions
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