Length Units

A length value is formed by an optional + or -, followed by a number, followed by a two-letter abbreviation that indicates the unit. There are no spaces in a length value; e.g., 1.3 em is not a valid length value, but 1.3em is valid. A length of 0 does not require the two-letter unit identifier.

Both relative and absolute length units are supported in CSS1. Relative units give a length relative to another length property, and are preferred since they will better adjust to different media. The following relative units are available:

· 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 length units are highly dependent on the output medium, and so are less useful than relative units. The following absolute units are available:

· in (inches; 1in=2.54cm)

· cm (centimeters; 1cm=10mm)

· mm (millimeters)

· pt (points; 1pt=1/72in)

· pc (picas; 1pc=12pt)