Email Signature Size Guide: Width, Logo, Headshot, and File-Size Numbers
Most broken-looking signatures are a sizing problem: too wide for phones, images too heavy, fonts drifting per device. Here are the numbers that work, and why.
Step by step
Total width: 320–600px, design for ~500
Desktop clients show ~600px comfortably; phones show ~320. A signature designed at 500px with a responsive max-width renders well everywhere. Wider = horizontal scrolling on phones.
Headshot: 64–100px displayed, 2× hosted
Display at 64–100px square; host the file at exactly double (128–200px) for Retina crispness. Bake the circle into the image itself — CSS circles die in Outlook.
Logo: 100–200px wide, exact dimensions in the HTML
Set explicit width AND height attributes — images without them are why logos render 'massive on my phone.' Host at 2× for Retina.
Banner: 500–600px wide, ~100–150px tall
Full-width of the signature, under 100KB. It's a billboard, not a hero image.
Fonts: 13–15px body, 16–18px name
Explicit pixel sizes on every element — unsized text inherits each device's defaults and drifts. Stick to email-safe stacks (Helvetica/Arial, system stacks).
File budget: every image under ~100KB, total under ~300KB
Heavy signatures slow message opens and trip spam heuristics. PNG for logos/graphics, JPEG for photos, nothing exotic (skip WebP/AVIF — client support is inconsistent).
Line count: 4–7
Name, title, company, contacts, maybe a CTA and disclaimer. Past seven lines you're writing a resume, not a signature.
The numbers are baked in
Autograph sizes, compresses, and hosts every image to these specs automatically — you pick the template, the math is already done.
Download Autograph free See the templatesCommon questions
Why does my logo look fine on desktop but huge on my phone?
No explicit width/height in the HTML — mobile clients scale unconstrained images to full width. Set the attributes (and a max-width) and it stops.
Is there a maximum signature size mail clients enforce?
No hard universal limit, but Gmail clips messages over ~102KB of HTML — a bloated signature eats that budget on every email. Stay lean.
Do I have to do this math myself?
Not if you use a tool that bakes it in — Autograph's templates carry all of these numbers (2× images, explicit dimensions, responsive stacking) by default.