You want to include advertisements on your site.
Design your pages to accommodate standard ad sizes.
If generating income is one of your web site's goals (see Recipe 2.1), then sooner or later your might consider running advertisements alongside your content to meet it. If you've determined that your site's content and traffic will support advertising, then you'll need a page layout designed to hold the ads. If it isn't, then you'll spend unnecessary effort reworking ads to fit your design or redesigning your site to fit the accepted sizes. Or worse—you won't get any advertisers.
Designing your pages to hold ads is only half the battle, if that. You'll find that many advertisers require specific placement on your pages. They will always want to be "above the fold" (i.e., visible without scrolling down), and balancing these requests without losing room for your content can be a real challenge.
Although there might be several hundred different sizes and shapes of "banner" ads on display on the web these days, the most common ones match the standard sizes established by the Interactive Advertising Bureau (IAB) in late 2002.
Large sites like Yahoo!, AOL, and CNET, all of whom are members of the IAB, use these sizes almost exclusively. Figure 3-4 shows the four sizes the IAB endorsed.
Figure 3-4. When placed in their usual locations ...