Email Signature Size Guide: Dimensions, Image Sizes & Best Practices

Sizing an email signature feels like it should be simple, but there are a few things that trip people up: Retina display scaling, Outlook resizing images unexpectedly, and signatures that look fine on desktop but are massive on mobile. This guide gives you the numbers that actually work.

Overall Width

Keep your signature 500–600px wide maximum. This is the sweet spot because:

• Most email clients render a reading pane around 600px wide
• Narrower signatures (under 400px) can look cramped with a logo on one side
• Wider signatures (over 650px) will get cut off or trigger horizontal scrolling in some clients

The 600px rule is the same constraint newsletter designers use, it's held true for 15+ years because email clients haven't fundamentally changed how they render HTML.

Height

Your entire signature, including logo, headshot, name, contact info, and any banners, should be under 200px tall. That's roughly 4–5 lines of text at normal size.

Why? Because the signature appears at the bottom of every message. If someone is reading a long email thread on their phone, a 400px signature is half the screen on each reply. It becomes noise that people scroll past, which makes the whole thing pointless.

Font Size

Don't use font sizes below 10px anywhere, they look invisible in some clients and get flagged by accessibility checkers. And stick to web-safe fonts or system fonts in the email: Arial, Helvetica, Georgia, or Times New Roman all render consistently. Custom fonts will fall back to Arial anyway.

Logo Size

Company logos in email signatures should be:

• Width: 100–200px (use the HTML width attribute, not CSS)
• Height: 40–80px depending on aspect ratio
• File format: PNG (supports transparency, looks sharp on Retina at 2x)
• File size: under 50KB, large images slow down email loading and can trigger spam filters

The trick for Retina displays: export your logo at 2x the display size, then specify the display size in the HTML. So if you want a 150px wide logo, export it at 300px wide and set width="150" in the HTML. It'll look crisp on Retina without appearing oversized on regular screens.

Headshot / Profile Photo

If you include a photo (common in real estate, consulting, and customer-facing roles):

• Display size: 60–80px (round or square both work)
• File size: under 30KB
• Aspect ratio: 1:1 (square), even if you're displaying it as a circle

Keep it professional, a clear headshot against a neutral background. A selfie or a cropped vacation photo will undermine an otherwise polished signature.

Banner Images (If You Use Them)

Some signatures include a banner below the contact info, often for a promotion, event, or award. If you use one:

• Width: 500–600px (matches the signature width)
• Height: 85–100px max
• Add an alt attribute, many clients block images by default, so the text fallback matters

Quick Reference Table