A certain trend among designers, believing that small text gives a Web page a sleek appearance and provides more space per “page” for actual content, sometimes results in the use of unreasonably small font sizes.

Unfortunately, this does not go well with the diversity of platforms used to access Web pages, from portable devices with tiny screens to projection devices hooked to computers. And even within a specific platform, text settings may vary.

The problem here is a basic usability and accessibility issue: a good design should look good without requiring the user to enlarge or reduce the text size.

Forget <font>, use CSS

The proper, modern way to set the size of the text displayed in a Web page is to use Cascading Style Sheets. This is strongly recommended over the use of <font> tags in HTML, because CSS is more flexible, easier to maintain and saves bandwidth. It is not the purpose of the Tip to discuss the interest of CSS versus <font> tags, readers wanting more details on this issue will ask their favorite Web search engine for related information… We will focus on good usage of the CSS technology to create legible Web pages.

Good usage of CSS’s font properties

Here are a few basic rules that one should follow in order to create Web pages that are easy (enough) to read, using CSS’s font properties.

Size: respect the users’ preferences, avoid small size for content

• As a base font size for a document, 1em (or 100%) is equivalent to setting the font size to the user’s preference. Use this as a basis for your font sizes, and avoid setting a smaller base font size
• Avoid sizes in em smaller than 1em for text body, except maybe for copyright statements or other kinds of “fine print.”

Units: avoid absolute length units for screen display

• Do not specify the font-size in pt, or other absolute length units for screen stylesheets. They render inconsistently across platforms and can’t be resized by the User Agent (e.g browser). Keep the usage of such units for styling on media with fixed and known physical properties (e.g print).
• Use relative length units such as percent or (better) em
• even better, if a base font-size is set for the document, use absolute size ([ xx-small | x-small | small | medium | large | x-large | xx-large ]) or relative size ([ larger | smaller ]) when defining the font size for a particular element within the document.

legible font-family

If using a small font-size, prefer a legible font-family with a high aspect value (see the section on font-size-adjust in the CSS2 specification for an explanation of the aspect value), which are more likely to be legible at such small sizes.