Blogger gives users the tools to customize their blog using graphics and text. Header images are one such form of graphics, usually stating the name of the blog and giving some measure of additional visual flair. Depending on the template used to create the blog, the header may need to confirm to a different width restriction. Height isn't any issue for Blogger headers.
Simple Layout
As its name implies, the "Simple" template is just that -- simple. A white workspace is framed by background imagery on the sides and bottom of the blog. When creating a header for this template, the maximum header width is 840 pixels. As with all Blogger templates, any height will do, but width beneath the maximum will leave blank space in the header, while widths exceeding this limit will be cut off at the side.
Picture Window and Watermark
The "Picture Window" template incorporates the header and blog description into the background, while actual posts are displayed on a small semi-transparent field in the center of the window. The "Watermark" template eschews a separate display field entirely, integrating text and the header into the background image. With both of these templates, maximum width for the header banner is 860 pixels wide.
Awesome Inc.
The "Awesome Inc." template incorporates the blog header and description into the background, and provides a semi-transparent display field for posts. The unchanged template utilizes contrasting dark backgrounds with bright text. When using the template, the maximum header size is 828 pixels wide.
Ethereal
The "Ethereal" template places a clean, white reading surface in the center of the page, bordered by two opposing background images to frame the blog. When using this template, keep in mind the maximum header width is 790 pixels.
Travel
The "Travel" template places a dark transparent text field over a background image, allowing the background to show through beneath the text, but not completely overshadowing it. When using this template, the maximum header width is 820 pixels.
Custom Templates
Users can also create their own templates and layouts using HTML and CSS code, as well as a number of custom tags created for use on Blogger. When creating your own layout, your header size is only limited by your imagination, but bear in mind not every screen will accommodate a gigantic 2,000-pixel-wide header.