Size attribute in CSS

Relative Units

em ems, the height of the element's font
ex x-height, the height of the letter "x"
px pixels, relative to the canvas resolution


Absolute Units

in inches; 1 inch = 2.54cms
cm centimeters; 1cm = 10mm
mm millimeters
pt points; 1pt = 1/72 inch
pc picas; 1pc = 12pts