Android长度单位

dp

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. The compiler accepts both "dip" and "dp", though "dp"
is more consistent with "sp".

sp

Scale-independent Pixels -
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 the
user's preference.

pt

Points - 1/72 of an inch based on the physical size of the screen.

px

Pixels - corresponds to actual pixels on the screen. This unit of
measure is not recommended because the actual representation can vary
across devices; each devices may have a different number of pixels per
inch and may have more or fewer total pixels available on the screen.

mm

Millimeters - based on the physical size of the screen.

in

Inches - based on the physical size of the screen.