CSS Length Units Reference

Relative length units
em	The height of the element's font.
ex	The height of the letter "x".
px	Pixels.
%	Percentage.
Absolute length units
in	Inches (1 inch = 2.54 centimeters).
cm	Centimeters.
mm	Millimeters.
pt	Points (1 point = 1/72 inches).
pc	Picas (1 pica = 12 points).