The font size or text size is the overall size (generally height) of a font shown on a screen or printed on a page. A font is typically measured in a point (pt) size, which is the vertical measurement of the lettering. There are approximately 72 (72.272) points in one inch or 2.54 cm. In the picture to the right, is examples of font sizes 6pt to 84pt.
The font size may also be measured in em space, which is the width of the font generally equal to the point size.
With web design and CSS a font size can be set as pre-determined font dimensions using: xx-small, x-small, small, medium, large, x-large, xx-large, smaller, or larger keywords. The font size can also be specified using the Point, Pica, Inch, Centimeter, Millimeter, em, and percentage.
Specifying the font size in an HTML tag
<p style="font-size:2em">This is an example of 2em</p>
Specifying the font size in CSS
In the example below, this CSS code would make any H2 tag on the page with a large font-size.