The short answer
Show it about 150 to 250 pixels wide and no more than 80 tall, but save the file at twice that size so it stays sharp. Use a PNG under about 50 KB.
The logo is the part of an email signature that goes wrong most often. It turns up enormous in someone's Outlook, blurry on an iPhone, or invisible in dark mode. Almost every one of those problems comes down to the size of the image file and how it was saved. Here are the numbers to use, and why.
The short answer
- A wide logo: shown at about 150 to 250 pixels wide.
- A square or round logo, or an icon: shown at about 60 to 100 pixels on each side.
- Height: no more than about 80 pixels, so the logo doesn't tower over your name.
- The whole signature: no wider than 600 pixels, so it fits on a phone without scrolling sideways.
- The file: saved at twice the size it's shown at, as a PNG, and ideally under 50 KB.
Why pixels, not centimetres?
Screens measure everything in pixels, the tiny dots that make up the picture. Your design software may show centimetres or inches, but when you export the logo, set its width in pixels. A logo 200 pixels wide takes up roughly the width of your name and job title written out, which is about right.
Why save it at twice the size?
Most phones and many laptops have high-density screens, which pack two or three dots into the space where an older screen had one. A logo saved at exactly 200 pixels wide looks soft on those screens. Save it at 400 pixels wide, then set it to display at 200 in the signature, and it stays sharp everywhere.
In Gmail, click the logo in the signature editor and choose a smaller size from the options that appear. In a designed HTML signature, the display width is written into the code. Either way, the file stays large enough to be sharp while showing at the right size.
Why does my logo look huge in Outlook?
This is the most common signature complaint, and it mostly happens in classic Outlook on Windows. That version can ignore the size you set in the signature and show the image at its real pixel size, especially on computers with display scaling turned on. So a 1,200-pixel logo you shrank in the editor suddenly fills the whole email.
There are two fixes. The simple one is to resize the image file itself to a sensible size before adding it, so even at its real size it isn't too big. The thorough one is a signature built in HTML with the width and height written into the image code, which Outlook respects. If most of your clients use Outlook at work, the second is worth having.
Which file format should I use?
- PNG for logos. It keeps edges crisp and supports see-through backgrounds.
- JPG for photos, like a headshot. It keeps the file small.
- Not SVG. It's ideal on websites, but Gmail and Outlook don't display it in emails.
- Not an animated GIF, unless you're sure of your readers. Classic Outlook only shows the first frame.
Watch out for dark mode
Lots of people read email in dark mode now. A dark logo saved on a see-through background sits on a black screen and disappears. Either save the logo with a white or light background built in (a rounded rectangle works well), or make a version with a thin light outline. Then send yourself a test email and look at it with dark mode switched on.
Sizes for other images in a signature
- Headshot: about 80 to 100 pixels square, often cropped to a circle. Saved at double size.
- Social media icons: about 20 to 24 pixels each, with a little space between them.
- A banner, for an event or offer: no wider than the signature, so up to 600 pixels, and short, around 100 pixels tall.
Does the file size matter?
Yes, more than people expect. Your signature goes out with every email, so a heavy image makes every message slower to load, especially on a phone with a weak signal. A logo should rarely need more than 50 KB. If yours is bigger, export it at the right pixel size and run it through a free image compressor before using it.
What if my logo doesn't work small?
Some logos have fine lines, small text or lots of detail that turns to mush at 200 pixels. If yours does, you may need a simpler version for small spaces, like just the symbol or initials. That's a common sign a logo needs a tidy-up; we cover others in five signs your logo is working against you.
A quick checklist
- Export the logo as a PNG at twice the width you want to show it at.
- Check the file is under about 50 KB.
- Add it to your signature and set it to display at half that width.
- Send a test to Gmail, Outlook and your phone.
- Check it again with dark mode on.
For the step-by-step setup, see how to add an email signature in Gmail and Outlook. If you'd rather have it done properly once, our email signature design is sized, tested in Gmail, Outlook and Apple Mail, and ready in a few days. If the logo itself needs work, start with logo design.
