The Tumblr Profile Banner size (3000×1055px)
A Tumblr profile banner is the wide header image at the top of your blog, and Tumblr recommends a large 3000x1055 pixel image. The generous width matters because Tumblr banners stretch across very wide desktop displays, and starting from a high-resolution master means the header stays sharp on big screens instead of looking soft or pixelated when the browser scales it up to fill the space.
The behavior to plan around is heavy responsive cropping. The banner is extremely wide relative to its height, and on narrower windows and mobile it gets trimmed inward toward the center, while your avatar and blog title sit over the lower-left portion of the header. To keep your design intact, place any key subject or text in the central band, away from the far left and right edges that disappear first and away from the lower-left where the profile elements overlap.
Sizing to the native 3000x1055 proportions prevents the distortion that happens when you drop a standard photo into such a wide slot, and it gives you control over which part of the image survives the crop. Because Tumblr blogs are highly personal and aesthetic-driven, a banner that matches your theme and mood sets the tone the moment someone lands on your page. This tool resizes 100% in your browser with no upload, it is free, and it preserves the aspect ratio. Tumblr can change its header dimensions and theme behavior, so verify the current spec before you redesign your blog.