Email Specs
Email Design Specs
Email design is constrained by rendering engines that predate most of the web platform, which is why the safe numbers below have barely moved in a decade. I would rather ship a template that renders identically everywhere than one that only looks good in Apple Mail.
| Item | Safe value | Why |
|---|---|---|
| Template width | 600px | Fits every major desktop preview pane |
| Maximum practical width | 640px | Some clients clip beyond this |
| Mobile stacking breakpoint | 480px | Common single column trigger |
| Header image width | 600px at 1200px export | Retina without breaking layout |
| Body padding | 20px to 24px | Readable on small screens |
| Item | Recommended value |
|---|---|
| Body font size | 16px minimum |
| Heading font size | 22px to 30px |
| Line height | 1.4 to 1.6 |
| Tap target size | 44px by 44px minimum |
| Font stack | Web safe fallback always declared |
| Item | Guidance |
|---|---|
| Total HTML size | Under 102KB to avoid Gmail clipping |
| Individual image size | Under 200KB where possible |
| Image formats | JPG, PNG, GIF, animated GIF |
| Background images | Not reliably supported in Outlook |
| Web fonts | Not supported in several major clients |
Notes
Gmail clips messages larger than roughly 102KB of HTML, hiding everything past the cut behind a View entire message link, and clipped content stops tracking correctly. Strip unused CSS, avoid inlining the same styles repeatedly, and check the raw size before every send.
Design for images off. A meaningful share of recipients see alt text before they see art, and some corporate clients block images by default. Every image needs real alt text, the call to action should be live HTML rather than a picture of a button, and the message must survive with no images at all.
Dark mode is the newest source of rendering surprises. Clients invert colours inconsistently, which turns black logos on transparent backgrounds invisible. Use PNG logos with a light stroke or a padded background, and test in Apple Mail and Outlook dark mode specifically.
Rendering behaviour changes as clients update, and Outlook in particular has multiple distinct rendering engines in active use. Test with a rendering service on every template change rather than assuming past results hold.
Frequently asked questions
Why is 600px still the standard email width?
Because desktop preview panes and older Outlook versions clip wider layouts. It is a legacy constraint, but the cost of ignoring it is broken layouts for the most valuable segment of many lists.
Can I use web fonts in email?
Partially. Apple Mail and some others support them, Outlook and Gmail largely do not. Always declare a full fallback stack and design so the fallback still looks intentional.
Is a single large image email ever acceptable?
No. It fails with images off, it is unreadable to screen readers, and it triggers spam heuristics. Use real text with images as support.
Official sources
Platforms change specifications without notice. Check the primary documentation before a launch that depends on an exact value.
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