Density-independent pixels (dp): Devices can have different resolutions. Resolution is defined by number of pixels per inch. Density independent pixels is a way to consistently measure the size of an image on a device independent of screen resolution. 320 dp is approximately 2 inches wide. dp = (width in pixels * 160) / screen density. E.g. for pixel density of 1 i.e. ~160 pixels per inch (iPhone 3) 320dp is 320px (320dp= (Xpx *160)/160). For pixel density of 2 i.e. 320 pixels (iPhone 5) 320dp is 640px (320dp= (Xpx *160)/320)