Email Signature Image Size

Email signature images have to look sharp on high-density screens while staying light enough not to bloat every message. The display size is what the recipient sees. A common range is up to 600 pixels wide for a banner, since most email layouts are around 600 pixels wide; 100 to 300 pixels wide for a logo; and 70 to 120 pixels square for a profile photo. The file itself is best exported at twice the display size, for example a logo shown at 200 pixels wide saved at 400 pixels and set to 200 in the HTML width attribute, so it stays crisp on retina displays. Without explicit width and height attributes, Outlook in particular may render the image at its native size, producing an oversized logo. File weight is the other limit: aim for under about 50 KB per image and around 100 KB for the whole signature, using PNG for logos with flat color or transparency and JPEG for photos. Hosted images, linked from a server, keep the email light, while attached or embedded images add their full size to every message and often appear as attachments. Every image should also carry alt text.