Android Icon Sizes

Current recommended launcher icon sizes in Android:

1. 48 x 48 (mdpi)
2. 72 x 72 (hdpi)
3. 96 x 96 (xhdpi)
4. 144 x 144 (xxhdpi)

There is also 36 x 36 for ldpi but the OS is able to resize that nicely from the better quality ones.

Reference: http://developer.android.com/design/style/iconography.html