Use relative font sizes

Requirement: Text sizes should be set using relative units such as percent or ems.

Many low-vision users make use of devices to enlarge content displayed on their monitors. By using relative font-sizes, these users are able to change the size of the text without much difficulty.

Font attributes should never be specified via the <font> element. This element has been deprecated. Instead developers should use markup and style sheets to control the appearance of text. Size should be defined by relative units such as percent, ems, exs. Do not use absolute units such as picas, inches, etc.

While not a requirement of Section 508 and categorized as a Priority 2 of the W3C's Web Content Accessibility Guidelines, the ease of implementing this standard and the benefit of it led its incorporation into the campus accessibility standard.

Other considerations about size

Generally, it is a good idea to use relative sizes when specifying the height and width of tables and so forth. This makes tables more accommodating across a range of computer monitors and resolutions. It gurantees that tables or frames can expand and contract for different users.

When determining the size of images, and images should always have a height and width specified, bear in mind that a typical maximized Web browser on typically configured 15-inch monitor will be just a little more than 580 pixels wide. If you set an image or table or other element to wider than 580 pixels, likely at least some of your users will have to scroll horizontally.

While 17-inch and larger monitors are more common today, many prefer not to maximize their browser. This is another reason why sticking to 580 pixels as the maximum horizontal width is a good idea. This width also translates closely to about the width of a letter-size sheet of paper on most monitors, helping ensure your pages will print reasonably.