Email signature banners can be a simple way to promote a webinar, new feature, discount, or booking link—without sending extra marketing emails. But if your banner is too big or the wrong format, it will look broken, blurry, or messy (especially on mobile).

This guide gives you practical banner sizes that work in real email clients—plus rules to avoid common problems.

Quick answer: best email signature banner sizes

Here are safe starting sizes:

Standard banner: 600 × 150 px
Small banner: 600 × 100 px
Tall banner (use carefully): 600 × 200 px
Retina / high quality export: 1200 × 300 px (displayed at 600 × 150)

Best file type: PNG (or JPG if photo-heavy)
Target file size: under 150 KB if possible

Rule: Keep the banner width around 600px. It fits most email layouts without forcing horizontal scrolling.

Why banner size matters in email signatures

Email clients are not like websites. They:

strip some HTML/CSS
block images by default sometimes
display different widths on different screens
change spacing when replying/forwarding

So the goal is not “perfect design.” The goal is “looks good in most clients, most of the time.”

Recommended banner dimensions (with examples)

1) Standard banner (best for most teams)

600 × 150 px (or 1200 × 300 for retina)
Works well for: product announcement, webinar promo, simple CTA

Optional image placeholder:

2) Small banner (best for clean, professional emails)

600 × 100 px
Works well for: “Book a demo,” “Try free,” “View pricing”

This is a great choice if you want the signature to feel professional, not “salesy.”

3) Taller banner (use only if you need it)

600 × 200 px
Works well for: event promo with date/time + CTA

Downside: tall banners push the email content down and can feel like an ad. Use only when needed.

Best width for Gmail and Outlook

Gmail

Gmail usually displays emails in a centered column. A banner around 600px wide generally fits well.

Outlook (desktop)

Outlook can be tricky. It may:

resize images
add weird spacing
handle DPI differently

To reduce problems:

export a retina version (1200px wide)
keep the design simple (large text, strong contrast)
avoid tiny text

If your banner has text, make the text big enough that it is readable on mobile.

File format: PNG vs JPG vs GIF

PNG (recommended)

Best for: text, logos, UI-style banners
Cleaner edges
Usually looks sharp

JPG

Best for: photo-heavy banners
Smaller file size in some cases
Can blur text if compressed too much

GIF

Works, but:
- can feel spammy
- can increase file size
- some email clients handle it poorly

For most teams: use PNG.

How to make banners look sharp (retina trick)

Export at 2× size for high-quality screens.

Example:

Design at 1200 × 300
Display as 600 × 150

This reduces blur in Outlook and on high-DPI screens.

What to put on a signature banner (simple and effective)

A banner should have one message and one action.

Good banner text examples:

“New: Team signature analytics”
“Webinar: Email signatures that drive demos”
“Book a 10-min setup call”
“Try it free — takes 2 minutes”

Good CTA styles:

“Book a demo”
“Start free”
“Watch the 2-min video”
“Get the template”

Keep words short. Most people will see the banner for 1–2 seconds.

Common banner mistakes (avoid these)

Mistake #1: Too much text

Small text becomes unreadable in email. Use fewer words, bigger font.

Mistake #2: Too many links

A banner should link to one page. Too many choices = fewer clicks.

Mistake #3: Large file size

Large images slow down loading and can get blocked. Compress the image and keep it under ~150 KB if you can.

Mistake #4: Low contrast

If text blends into the background, it won’t be readable. Use strong contrast.

Mistake #5: Always-on banners

Campaign banners work best when they rotate:

run a campaign for 2–4 weeks
then remove it or replace it

Where should the banner go in the signature?

Best placement:

Contact details (name/title/company)
Banner
Small spacing
Legal line (if needed)

This keeps the banner visible but not in the middle of your identity info.

How to track banner clicks (so you can improve)

If you never track clicks, you’re guessing.

Track using:

UTM parameters (easy)
signature analytics tools (better for teams)

Example UTM link:

?utm_source=email-signature&utm_medium=banner&utm_campaign=webinar

Then you can see performance in your analytics tool.

FAQ: Email signature banner size

What is the best email signature banner width?

600px is a safe width for most email clients.

What is the best height?

For most banners: 100–150px.

Should I use 2× retina size?

Yes. Create at 1200px wide and display at 600px wide for sharper results.

What file type is best?

PNG is best for sharp text and logos.

Can I use an animated GIF banner?

You can, but it can feel spammy and may increase file size. Use carefully.

Summary

If you want a banner that looks professional and works in Gmail and Outlook, start with 600 × 100 or 600 × 150, export a retina version for sharpness, keep file size small, and use one simple CTA.