Android supports multiple units of measurement (such as Pixels, inches, millimeters, points etc). However the following two units of measurement are critical for a good design:
- Density-independent Pixels (dp) - an abstract unit that is based on the physical density of the screen. These units are relative to a 160 dpi screen, so one dp is one pixel on a 160 dpi screen. The ratio of dp-to-pixel will change with the screen density, but not necessarily in direct proportion.
- Scale-independent Pixels (sp) - this is like the dp unit, but it is also scaled by the user's font size preference. It is recommend you use this unit when specifying font sizes, so they will be adjusted for both the screen density and user's preference.
As a best practice, never use anything but sp or dp unless you absolutely have to. Using sp/dp will make your Android applications compatible with multiple screen densities and resolutions.