What size should an email signature banner be?
600 × 150 pixels is a strong starting point: it matches the widths most email layouts are built around and leaves room for a logo, a headline and a button. Use 600 × 100 when you only have one line to say, and 600 × 200 when the design needs more vertical space. Export at the size you designed rather than resizing the image inside your mail client.
Key facts
- Recommended size
- 600 × 150 px for a standard email signature banner.
- Compact option
- 600 × 100 px when the banner carries one line of copy.
- Roomy option
- 600 × 200 px when you need a logo plus two lines and a button.
- Maximum sensible width
- 600 px — wider banners get scaled down by most reading panes.
- Aspect ratio
- Between 3:1 and 6:1, so the banner never dominates the message.
Why 600 pixels wide
600px is the width email templates have been built around for years, because it fits comfortably in a desktop reading pane without horizontal scrolling. Signature banners inherit that convention. Going much wider risks being clipped or scaled down unpredictably; going much narrower wastes the space.
Treat it as a strong starting point rather than a rule handed down from the email clients themselves. No client publishes an official signature banner dimension.
The three sizes to choose between
| Size | Ratio | Best for |
|---|---|---|
| 600 × 150 | 4:1 | The default. Logo, headline, supporting line and a CTA button. |
| 600 × 100 | 6:1 | One short line plus a button. Keeps signatures compact on mobile. |
| 600 × 200 | 3:1 | Bigger logo, two lines of copy, or a product-led design. |
- Ratio
- 4:1
- Best for
- The default. Logo, headline, supporting line and a CTA button.
- Ratio
- 6:1
- Best for
- One short line plus a button. Keeps signatures compact on mobile.
- Ratio
- 3:1
- Best for
- Bigger logo, two lines of copy, or a product-led design.
A practical starting size for email signature promotional banners.
How the banner behaves on mobile
Phone mail apps scale the image down to the screen width. A 600px-wide banner might render around 320–400px across. That is the real readability test: if your supporting line is small on the canvas, it will be very small on a phone.
- Keep the headline to roughly six words or fewer.
- Avoid text below about 12px at the canvas size — it will not survive scaling.
- Keep the CTA a solid pill with high contrast so it still reads as a button when small.
- Leave breathing room at the edges; some clients crop by a pixel or two.
Retina and export scale
High-density screens can make an image designed at exactly its display size look soft. The usual fix is to export larger and display smaller — for example produce the artwork at twice the size and set the displayed width to 600px in the signature HTML.
There is a trade-off: larger exports mean larger files, and GIF file size grows fast with animation. If your banner is animated, favour a smaller, cleaner design over a huge crisp one.
Common sizing mistakes
Resizing the image after inserting it
Dragging the corner in Gmail or Outlook is the most common cause of blurry signature banners. Change the canvas size in the editor and export again instead.
Designing a square banner
Square images push your signature and the reply thread down the screen. Wide and short is the shape that fits how people read email.
Copying a web hero image into a signature
A hero image is designed to be seen at 1200px+ with plenty of hierarchy. At 600px the text usually disappears. Rebuild it as a banner.
Filling every pixel
Whitespace is what makes a small banner readable. Aim for one message, one supporting line and one button.
Key terms
- Email signature banner size
- Email signature banner size is the pixel width and height of the promotional image in a signature — 600 × 150 px is the common default.
- Retina export
- A retina export is an image rendered at twice the display dimensions so it stays sharp on high-density screens.
- Aspect ratio
- Aspect ratio is the relationship between an image's width and height, written as width:height.
Common questions
No. Email clients do not publish a required size. 600 × 150 is a widely used convention because email layouts are built around a 600px width.