Length Units

Absolute Relative
Unit Meaning Unit Meaning
in inches em ems (height of element's font)
cm centimeters ex x-height (height of letter 'X')
mm millimeters px pixels (relative to canvas)
pt points (1/72 inch) % percent (usually of element)
pc picas (12 point)

These are the units which can be used in Cascading Style Sheets.