Guides
Email Signature Size & Dimensions: The Complete Guide (2026)
The right email signature dimensions, image sizes, and file weight for Gmail and Outlook — so your signature looks sharp on desktop and mobile without getting cropped.
The recommended email signature size is 300–600px wide and 90–150px tall, with the whole thing kept under 100KB. Logos and images inside it should be no more than about 400px wide, saved as PNG (for logos) or JPG (for photos). Stay inside those numbers and your signature renders cleanly on desktop and mobile without getting cropped, blurry, or flagged as an attachment.
Here’s the full breakdown, including why each limit exists and the numbers that differ between Gmail and Outlook.
Recommended email signature dimensions
| Element | Recommended size | Hard limit |
|---|---|---|
| Overall signature width | 300–600px | Keep under 650px |
| Overall signature height | 90–150px | Under ~200px |
| Logo / image width | 150–400px | Under 400px |
| Logo / image height | 70–100px | Under 150px |
| Headshot (if used) | 80–100px square | Under 150px |
| Total file weight | Under 100KB | Under 1MB |
The single most important rule: keep the total width at or under about 600px. Most email clients render the reading pane at roughly 600px, and anything wider gets cropped or force-scaled — which is what makes signatures look broken on a phone.
Why size matters more than it looks
A signature that’s too big fails in three ways:
- It gets cropped on mobile. Over half of email is opened on a phone. A 700px-wide signature simply won’t fit, so the right edge — often your CTA or phone number — disappears.
- Heavy images load slowly or get blocked. Large embedded images can trigger “download pictures” prompts or land in spam-flagging territory. Under 100KB keeps things instant.
- Embedded images become attachments. If an image is embedded rather than hosted, some clients show it as a paperclip attachment, which looks unprofessional and clutters the thread.
Image format: PNG vs JPG
- PNG — use for logos, icons, and anything with a transparent background or sharp edges/text. It stays crisp and supports transparency.
- JPG — use for photos and headshots. It compresses richer images to a smaller file size.
- Avoid BMP and TIFF (huge) and be cautious with animated GIFs (many clients, including some Outlook versions, don’t animate them and may show only the first frame).
Always host images on a stable URL and reference them, rather than embedding, so they don’t attach to the message and always resolve.
Gmail vs Outlook: the size differences
The clients render slightly differently, so the sweet spots differ:
| Gmail | Outlook | |
|---|---|---|
| Best logo width | up to ~200px | up to ~200px |
| Best logo height | ~80px | ~170px |
| Renders images by | Google image proxy (resized/cached) | Direct, with stricter HTML/CSS support |
| Common gotcha | image auto-scaling | dropped CSS, extra spacing around tables |
Outlook (especially older Windows versions) is the strict one: it uses Word’s rendering engine for HTML, so complex CSS gets ignored. Keep layouts simple — table-based, inline styles, no fancy positioning — and test in Outlook specifically. Adding your signature is covered step by step in how to add a signature in Outlook and how to add a signature in Gmail.
Retina and resolution: serve images at 2×
Modern screens are high-density, so an image displayed at 200px looks sharper if the actual file is 400px wide and constrained to 200px in the HTML (width="200"). You get crisp rendering without increasing the displayed size. Just keep the file under the weight limits above.
A quick pre-send checklist
- Total width ≤ 600px
- Logo ≤ 400px wide, under 100KB
- Images hosted on a URL, not embedded
- PNG for logo, JPG for photo
- Tested on mobile and in Outlook
- Reply version is short (no giant logo on every reply)
The hard part: keeping every signature to spec
Getting the dimensions right for your signature is a one-time job. Getting them right for everyone on your team — and keeping them there as people join, change roles, or paste in their own oversized logo — is the real problem. One person’s 900px banner breaks the consistency you worked to build.
That’s the case for managing signatures centrally. With Firma, you design one correctly-sized, on-brand signature and deploy it across every Gmail or Google Workspace account, so the dimensions, images, and layout stay within spec for the whole team automatically. See email signature management for how that works, or browse signature examples sized correctly out of the box.
Frequently asked questions
What is the ideal email signature width? Keep the overall signature at or under 600px wide, since that’s roughly the width of most email reading panes. 300–500px is a comfortable target.
How big should a logo be in an email signature? No more than about 400px wide and 150px tall, saved under 100KB. For display, constraining a 2× image (e.g. a 400px file shown at 200px) keeps it sharp on high-resolution screens.
What file size should an email signature be? Aim to keep the whole signature — all images combined — under 100KB so it loads instantly and doesn’t trigger image-blocking or spam heuristics.
Should I use PNG or JPG? PNG for logos and anything with transparency or crisp text; JPG for photographs and headshots.
Why does my signature look broken on mobile? Almost always because it’s too wide. If the signature exceeds ~600px, phones crop or rescale it. Reduce the width and test on a phone before rolling it out.
Cristian Cabrera, Founder of Firma
I built Firma so your team can have beautiful, consistent, professional email signatures — while you drink your coffee ☕️ instead of setting them up by hand for every new hire. It works like a charm with Google Workspace and Microsoft 365, and it doubles as a new marketing channel — announce a launch or promo right from everyone's signature. 😍 Here's my LinkedIn if you'd like to connect.