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)

MultiLength and MultiLengths

MultiLength attribute values may be an integer in pixels, a percentage of the horizontal or vertical space, or a relative length expressed as i* where i is an integer. In allotting space, a browser first allots pixel and percentage lengths, then divides the remaining space among all elements with a relative length. An element with a length of 3* will be allotted three times the space of an element with length 1*. The value * is equivalent to 1* and is often used to mean "fill the remaining space."

A MultiLengths value is a comma-separated list of MultiLength values.