What is the difference between "px", "dip", "dp" and "sp"?

Question

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Answer 1

From the Android Developer Documentation: px Pixels - corresponds to actual pixels on the screen. in Inches - based on the physical size of the screen. 1 Inch OR 2.54 centimeters mm > Millimeters - based on the physical size of the screen. pt > Points - 1/72 of an inch based on the physical size of the screen. dp or dip > Density-independent Pixels - 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. Note: The compiler accepts both "dip" and "dp", though "dp" is more consistent with "sp". sp > Scaleable Pixels OR scale-independent pixels - this is like the dp unit, but it is also scaled by the user's font size preference. It is recommended you use this unit when specifying font sizes, so they will be adjusted for both the screen density and the user's preference. Note, the Android documentation is inconsistent on what sp actually stands for, one doc says "scale-independent pixels", the other says "scaleable pixels". From Understanding Density Independence In Android: Density Bucket Screen Density Physical Size Pixel Size ldpi 120 dpi 0.5 x 0.5 in 0.5 in * 120 dpi = 60x60 px mdpi 160 dpi 0.5 x 0.5 in 0.5 in * 160 dpi = 80x80 px hdpi 240 dpi 0.5 x 0.5 in 0.5 in * 240 dpi = 120x120 px xhdpi 320 dpi 0.5 x 0.5 in 0.5 in * 320 dpi = 160x160 px xxhdpi 480 dpi 0.5 x 0.5 in 0.5 in * 480 dpi = 240x240 px xxxhdpi 640 dpi 0.5 x 0.5 in 0.5 in * 640 dpi = 320x320 px Unit Description Units Per Physical Inch Density Independent? Same Physical Size On Every Screen? px Pixels Varies No No in Inches 1 Yes Yes mm Millimeters 25.4 Yes Yes pt Points 72 Yes Yes dp Density Independent Pixels ~160 Yes No sp Scale Independent Pixels ~160 Yes No More info can be also be found in the Google Design Documentation.