Email Signature Logo Size: Dimensions, Format and File Weight

Quick answer: show a signature logo about 40 to 100 pixels high, with Google's published range for Gmail signature images being 70 to 100 pixels high and 300 to 400 wide (maximum 100 by 1,000). Export the file at twice the displayed size as a PNG, set the width and height attributes, and keep it under about 50KB.

A logo is a supporting detail in a signature, not the main event. It should be sharp, light and still visible when the recipient uses dark mode, and it should not push your name and phone number down the screen.

How big should a logo be in an email signature?

• Google recommends signature images of about 70 to 100 pixels high and 300 to 400 wide, with a maximum of 100 pixels high by 1,000 wide.
• Most signature logos sit at the smaller end of that range. In Email Signature Magic's layouts a logo is shown at no more than about 40 pixels high, which keeps a signature compact and light.
• Whatever you choose, keep the whole signature at about 600 pixels wide or less.

Export at twice the size, display at half

To stay sharp on high-resolution screens, export the logo at about twice the size it will be displayed, then set the image's width and height attributes to the display size. Outlook does not support CSS widths and heights, so the attributes are what keep a large file from appearing huge there.

PNG, JPG or SVG?

Use PNG for a logo, because it handles flat colors and transparency cleanly. JPG suits photographs. SVG support in email is inconsistent, and Outlook's desktop renderer in particular does not reliably display SVG images, so a PNG is the safe choice.

Make sure it survives dark mode

A logo with dark text on a transparent background can vanish on a dark screen. Litmus recommends adding a light outline or glow to transparent PNGs with dark text, or supplying separate light and dark versions. A logo on a white or light plate always reads, at the cost of looking like a patch on dark screens, so test both.

Keep the file light

Heavy images slow every email and can be downscaled unpredictably. Aim for a logo well under 50KB and a whole signature under about 150KB. A logo saved straight from a website at several thousand pixels wide is the usual culprit, so resize before you upload.

Give it real alt text

Use your company name as the alt text. Outlook blocks automatic picture downloads by default, and spam filters score an image with no alt text as a minor risk, so the alt text both shows when the picture doesn't and keeps the signature clean.