Why should we use sp for font sizes in Android? [duplicate]

Answer 1

Sp is scaled independently with respect to the normal font size of the device. http://developer.android.com/guide/practices/screens_support.html

Similarly, you should prefer the sp (scale-independent pixel) to define text sizes. The sp scale factor depends on a user setting and the system scales the size the same as it does for dp.

Answer 2

The dp has constant ratio transition to px: dp = px * ratio. Where ratio will never change on any particular device.

While sp (s for scaled) has scalable ratio: sp = px * ratio * scale. Where ratio never changes, but scale is user configurable. This scale can be used by people who need larger font sizes, for example, to use device more comfortably.