Email Signature Image Size Guide
Email signature images have three separate constraints: pixel dimensions (how large they appear), file size (how long they take to load), and hosting requirements (where they must be served from). Outlook also has a DPI scaling bug that enlarges images on high-resolution displays unless you apply a specific HTML fix.
Quick Reference
Dimension Specifications by Image Type
Square crop. PNG or JPG. Keep under 30KB. Larger headshots (120px+) push signature content far right on mobile and can overflow narrow email views.
PNG with transparent background preferred. Max height 60px keeps the logo from dominating the signature. Wider logos (wordmarks) can go to 200px; icon-only marks should be 40–60px square.
PNG or SVG. Keep all icons the same pixel size for alignment. A row of 5 icons at 24px each spans ~140px with spacing — fits on all screen sizes.
Use sparingly. Banners push the signature below the fold in many preview panes. If used, host on a CDN with HTTPS. Animated GIFs are supported by Gmail and Apple Mail but blocked by Outlook (shows first frame only).
Can be a 1px tall image or a CSS border-bottom on a table row. CSS borders are safer: no image request, zero load time, renders in all clients.
File Size and Format
PNG
Use for logos, icons, and anything with transparency or sharp edges. Lossless compression — edges stay crisp. A 200px logo PNG should be under 15KB after compression. Use tools like Squoosh or TinyPNG before hosting.
JPG
Use for headshots and photos. Lossy compression handles photographs better than PNG. Export at 80–85% quality — visually lossless but 60–70% smaller than uncompressed. Target under 30KB for a 100px headshot.
SVG
Supported in webmail clients (Gmail, OWA) but not in desktop Outlook or many mobile email apps. If you use SVG social icons, test in Outlook — they will not render and the space will be empty.
GIF (animated)
Gmail, Apple Mail, and Thunderbird render animated GIFs. Outlook displays only the first frame. If your first frame is a complete, meaningful image (not blank), animated GIFs in banners are acceptable — just ensure first-frame fallback looks correct.
The Outlook DPI Scaling Fix
On Windows displays set to 125% or 150% scaling (common on laptops and 4K monitors), Outlook scales images up proportionally — so a 100px image renders at 125px or 150px, breaking your layout. The fix requires specifying width in both the HTML attribute and inline CSS:
The HTML width attribute overrides DPI scaling in Outlook. The CSS max-width prevents overflow in Gmail and webmail. Both are required — neither alone is sufficient across all clients.
Hosting Requirements
HTTPS required
Images served over HTTP are blocked by most email clients (marked as insecure content). Use HTTPS hosting — GitHub Pages, Cloudflare Pages, Vercel, or any CDN with SSL all work.
No base64 in Gmail signatures
Gmail strips base64-encoded inline images from signatures specifically (they work in email body but not signature blocks). Images must be at external URLs.
Gmail re-hosts images
Gmail proxies external images through its own CDN (lh3.googleusercontent.com or ci3.googleusercontent.com). This is normal — the images still display. It means image URL changes after initial load won't update for recipients who have cached the email.
Avoid corporate file storage
SharePoint, OneDrive, Google Drive, and Dropbox URLs are not reliably public. Links time out, require auth, or change format. Use a proper web host or CDN.
Related Guides
Generate a Signature with Correctly Sized Images
SignForge applies the Outlook DPI fix automatically — both width attribute and inline CSS on every image.
Create My Signature →Works with Gmail, Outlook, Apple Mail & more