We saw a lot of banners on almost every webpage.
Here is a standard for website designer.
Rectangles and Pop-Ups
300 x 250 IMU – (Medium Rectangle)
250 x 250 IMU – (Square Pop-Up)
240 x 400 IMU – (Vertical Rectangle)
336 x 280 IMU – (Large Rectangle)
180 x 150 IMU – (Rectangle)
Banners and Buttons
468 x 60 IMU – (Full Banner)
234 x 60 IMU – (Half Banner)
88 x 31 IMU – (Micro Bar)
120 x 90 IMU – (Button 1)
120 x 60 IMU – (Button 2)
120 x 240 IMU – (Vertical Banner)
125 x 125 IMU – (Square Button)
728 x 90 IMU – (Leaderboard)
Skyscrapers
160 x 600 IMU – (Wide Skyscraper)
120 x 600 IMU – (Skyscraper)
300 x 600 IMU – (Half Page Ad)
It is very useful when designing a new layout of Website.
Please see the IAB, Interactive Advertising Bureau.