Correct Email Signature Dimensions: Width, Height & File Size
Width, height, image file size, and Retina tips — everything brand and marketing teams need before building a new signature. See the full spec guide
Short answer
What are the correct dimensions for an email signature?
Email signature dimensions should be 300-400px wide and 150-200px tall. Keep all image files under 100KB in JPG or PNG format. Anything wider than 400px gets cropped or rescaled on mobile screens, breaking the layout your recipients actually see.
Short Answer
What are the correct dimensions for an email signature?
Email signature dimensions should be 300-400px wide and 150-200px tall. Keep all image files under 100KB in JPG or PNG format. Anything wider than 400px gets cropped or rescaled on mobile screens, breaking the layout your recipients actually see.
Generate your perfect email signature →
Signature Size Mistakes
When wrong email signature dimensions break your brand
Email signature dimensions above 400px in width get truncated or rescaled by Gmail, Outlook, and Apple Mail on mobile screens. The layout you carefully built on desktop does not transfer.
This is one of the most common brand presentation mistakes marketing teams discover after the fact, when off-spec signatures have already reached prospects and clients.
Getting dimensions right before design is a 5-minute spec check that prevents weeks of cleanup.
Email Signature Width And Height
What width and height should an email signature be?
Email signature width should stay between 300 and 400px. Most email clients scale signatures to fit their viewing pane, which means anything wider produces a smaller, compressed result on phones and tablets.
Email signature height should stay between 150 and 200px. This is a softer limit than width, but signatures that run taller signal information overload and distract from the email itself.
If your signature content is long, build it vertically rather than horizontally. Use a maximum of 2 columns, 3 at the absolute limit. Never exceed 3 columns in an email signature layout.
Image File Size And Format
What image file size should an email signature stay under?
Email signature images should stay under 100KB per file. Gmail limits the full HTML signature to 10,000 characters; Outlook limits it to 8,000.
But the practical constraint is image file size: heavy images fail to load, leaving recipients looking at broken layout boxes instead of your logo.
Use PNG for logos and anything with a transparent background. Use JPG for photos. Avoid animated GIFs unless they’re essential to your design since they add file weight fast.
2 techniques keep image size down:
- Link to hosted images rather than embedding them as attachments. The image loads from a URL each time the email opens, adding zero weight to the HTML.
- Compress images before uploading. Free tools like TinyPNG reduce file size by 60-80% without visible quality loss.
If you build signatures in WiseStamp’s Studio Editor, image compression and hosting are handled automatically on upload. You stay under the 100KB threshold without manually optimizing each file.
signature HTML character limit
What is the character limit for an HTML email signature?
Every email client caps how much HTML your signature can contain. Gmail famously allows up to 10,000 characters but other email clients may be much more restrictive.
It’s important to note that the character limit is not something you can play with. It’s a hard stop. An HTML signature that crosses the hard limit will Prevent the email signature from being saved, or, worse yet, it will display the email signature broken.
Email signature HTML character limit by email client:
| Email Client | Limit | Type |
|---|---|---|
| Outlook (classic) | 10,000 characters | HTML character limit |
| Outlook (new / 365) | 8,192 characters | HTML character limit |
| Microsoft 365 (OWA) | 8,192 characters | HTML character limit |
| Gmail | 10,000 characters | HTML character limit |
| Apple Mail | Less than 100 KB | Image file size |
| AOL Mail | 1,000 characters | HTML character limit |
| Yahoo Mail | 1,000 characters | HTML character limit |
| Thunderbird | Below 150 KB | Image file size |
Hosting images externally rather than embedding them keeps your HTML count low across all clients.
Retina Display Optimization
How should you size email signature images for Retina and HiDPI displays?
Retina displays (standard on modern MacBooks, iPhones, and iPads) render images at 2x pixel density. To keep your logo and photos sharp on these screens, upload images at exactly twice the display size.
If your logo displays at 150px wide in the signature, upload it at 300px wide, then set its display width to 150px in the template. This exact doubling prevents blurring. Approximate scaling does not.
Takeaway
Email signature size and dimensions best practices
Email signature dimensions that render correctly across Gmail, Outlook, and Apple Mail: 300-400px wide, 150-200px tall, with images under 100KB in PNG or JPG format.
Limit columns to 2-3. For Retina displays, upload images at exactly double their display size.
“WiseStamp creates professional, visually appealing signatures without needing design or coding skills.”
Jessica C., Director of Marketing at a mid-market company
The specs above are the foundation for that outcome.