FontSize

FontSize is an option for Cell, StyleBox and StyleForm which specifies the default size in printer's points of the font in which to render text.

The size of a font is typically taken to be the distance from the top of the highest character to the bottom of the lowest character.

A printer's point is approximately of an inch.

Fonts with the same nominal point size may not look the same size to the eye.

See The Mathematica Book: Section 2.8.9 and Section 2.10.10.

See also: FontWeight, FontTracking, ScriptMinSize, ScriptSizeMultipliers.