Screen resolutions and image ratios of Android devices

The base resolution(1.0) is mdpi, and ratios of other resolutions are below.
ldpi = 0.75
mdpi = 1.00
hdpi = 1.5
xhdpi = 2.0
xxhdpi = 3.0
xxxhdpi = 4.0

Width for each resolution of an image which width is 100px
ldpi = 75px
mdpi = 100px
hdpi = 150px
xhdpi = 200px
xxhdpi = 300px
xxxhdpi = 400px

Supporting Multiple Screens | Android Developers