For Android launcher icons you will need 6 sizes of PNG or JPG files. In pixels these are
48×48,
72×72,
96×96,
144×144,
192×192
512×512.
The first five are for the App and the last one for when the App is deployed to the Google Play store. These are the final size of the icons and you must allow for a small margin, hence the area the icon is drawn in will be a bit smaller. For low density screens Android halves the 72×72 icon, but it is possible to include a 36×36 icon in the App for completeness, making 7 icons in total. An Android icon size table in this article summarizes all the relevant information.
