Email Signature Size Guide: Dimensions, Image Sizes, and File Weight

Why size is a real constraint

Size sounds like a cosmetic detail, but in email it is a functional one. Get it wrong and signatures get clipped, load slowly on mobile data, blur on high-resolution screens, or disappear entirely when a client refuses to download a heavy image. This guide covers the dimensions and weights that keep a signature sharp, fast, and intact across inboxes.

Overall width

Design your signature for a maximum of about 600 pixels wide. That is the traditional safe width for the email body, and staying at or below it avoids horizontal scrolling. In practice, many of the cleanest signatures are narrower still — 300 to 500 pixels — which adapts more gracefully to phones, where most email is now read. If you use a fixed-width table, keep that width modest and let the content breathe rather than stretching edge to edge.

Logo and image dimensions

Display size

A logo typically looks right at roughly 40 to 90 pixels tall, sized so it sits comfortably beside your text without dwarfing it. A headshot usually works around 80 to 120 pixels square. Set the intended display width and height directly on the image tag — Outlook in particular needs those attributes, or it may show the image at full native size.

Export at 2x for sharp screens

Retina and other high-resolution displays pack more physical pixels into the same space, so an image exported at its exact display size can look soft. The fix is to export the source at double the display dimensions, then set the width and height attributes to the intended (1x) size. A logo shown at 200x60 should be exported at 400x120. It stays crisp on retina screens without appearing oversized anywhere.

File format

Use PNG for logos and anything needing transparency, and JPG for photographs, where it compresses better. Avoid SVG — Gmail and Outlook do not support it in email, so a vector logo will simply fail to appear. Stick to raster formats that every client understands.

File weight is where signatures quietly fail

Keep each image small

Aim to keep a logo well under 50KB, and ideally closer to 20KB, after compression. Large images load slowly on mobile data and are more likely to be blocked or deferred by the client. Run every image through a compressor before you use it.

The 102KB rule in Gmail

Gmail clips messages larger than roughly 102KB, showing a "[Message clipped]" link and hiding everything past that point — which frequently includes your signature. Since that budget covers the entire message, not just the signature, bloated signature HTML and heavy embedded images push you toward the limit fast. Lean, table-based HTML with externally referenced (not base64-embedded) images keeps you comfortably under it.

Pixels versus points

Outlook's Word-based engine has a long history of converting pixel values to points and rounding as it goes, which can throw sizing off by a hair. Specify image dimensions in plain pixels on the tag, keep values simple, and test in Outlook rather than trusting that the numbers you typed are the numbers it renders.

Font sizes for legibility

• Name: around 16–18px, so it leads the hierarchy.
• Title, company, and contact details: around 12–14px.
• Disclaimers or fine print: no smaller than 10–11px, or it becomes unreadable, especially on mobile.

Quick reference

1. Overall width: 600px maximum, less is often better.
2. Logo: ~40–90px tall on display, exported at 2x.
3. Headshot: ~80–120px, exported at 2x.
4. Per image: under ~50KB after compression.
5. Whole message: under 102KB to avoid Gmail clipping.
6. Formats: PNG or JPG, never SVG.
7. Body text: 12–14px; name larger; fine print no smaller than 10px.

Hitting all of these by hand takes some care, particularly the file-weight math. A generator such as Sigmint produces lean HTML and appropriately sized images by default, which keeps you clear of the clipping threshold without manual optimization. Whichever route you take, remember that in email, lighter is almost always better.