From Nielsen Online, this chart and table show which banner ad sizes are used the most on U.S. websites.

This information should be taken as only one indicator among many, and may not apply to your site. On a national/global scale, clearly bigger is better ... but few local websites use Leaderboards or Skyscrapers.

There is a concern that the fourth most popular size - actually a collection of sizes - comprises non-standard dimensions. We strongly encourage you to use ad sizes that conform to the standards of the Interactive Advertising Bureau. It will make your web design process easier, and it will facilitate selling banners to larger and/or more sophisticated advertisers.

 

Dimensions				Unique Ads
		Leaderboard (728x90)		24,091
		Medium Rectangle (300x250)		22,237
		Wide Skyscraper (160x600)		13,645
		Non-Standard Dimension		10,125
		Full Banner (468x60)		2,302
		Skyscraper (120x600)		2,248
		Large Rectangle (336x280)		2,100
		Rectangle (180x150)		1,762
		Button #2 (120x60)		1,214
		Half Banner (234x60)		1,077
		Other		3,737
		Total		84,538