If you are creating advert banners and buttons for your website you should make them according to the following sizes.

Below is a table of standard banner sizes used on most web sites. You don't have to use these sizes but they have become a convention and systems such as Google's Adsense tend to use them.

At the end of this article you can download a zip file containing examples of all the different banner sizes. These are useful to place into a web site design so you can seen how various types of advert will look within your page layout.

Use the example link to popup an example png graphic.

Here is a zip file containing example banner adverts in all the above sizes. They are PNG images :
standard_web_banner_advert_sizes.zip