Pixels (px) (Absolute) One pixel equals one physical pixel on a computer display.

Points (Absolute) on the Mac, one point is equal to 1/72 of an inch. On windows, it’s 1/96 of an inch.

Picas (Absolute) One pica is equals to 12 pts.

Inches One inch is equal to 2.54 centimeters. (used for typographical properties other than font size such as line height, text indent, letter spacing, etc.)

Centimeters One centimeter is equal to almost 2 /5 of an inch. (used for typographical properties other than font size such as line height, text indent, letter spacing, etc.)

Millimeters 10 millimeters are equal to one centimeter. (used for typographical properties other than font size such as line height, text indent, letter spacing, etc.)

EMS (Relative) EMS are measured relative to the parent (inherited) font size. If inherited font size is 12 point. 1 em will equal 12 pts. 2 em would result in 24 pt. text.

X-height (Relative) Defined by the size of the current font’s x character, or the size of the x character of the inherited font size. .

Percent (Relative) One Based on the computed value of an inherited length.