The Mastodon Profile Header size (1500×500px)
The Mastodon profile header is the wide banner across the top of your profile, and 1500x500 at a 3:1 ratio is the widely recommended size across the fediverse. Mastodon is decentralized, so your profile can be viewed from many different instances and apps, and 1500x500 is the safe common denominator that renders correctly whether someone sees you through the web interface or a third-party client.
That 3:1 banner shape gives you a horizontal strip to set the tone of your profile, but the way Mastodon lays out the page affects it: your circular avatar overlaps the lower-left of the header, and profile text can sit over the banner in some clients. Because of that, keep important elements like text or a logo toward the center-right and away from the bottom-left, where the avatar and metadata will cover them.
Different instances apply slightly different display sizes and some compress uploads, so exporting at a clean 1500x500 gives the best chance of a sharp result rather than a soft or oddly cropped banner. A calm, on-brand image that complements your avatar makes the profile feel considered, which matters on a platform where your header is part of how a community decides to follow you. Everything here resizes 100% in your browser with no upload and for free, so your banner stays private on your device. Mastodon instances vary and update their handling, so verify how yours renders headers before finalizing.