Below are some of the standard banner sizes used on web pages. It is a sort of convention to develop banners based on these sizes; however, we are not bound by these dimensions, as it were. Two other sizes for banners are also in use: 350x300 and 720x300. These are generally not used on web pages but as pop-up or pop-under ads displayed on separate browser windows.
the standard sizes for banners have been formulated by the internet advertising bureau.