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Chapter Thirteen. Working with Browsers ... > A Standard Size at Last—But for How ...

A Standard Size at Last—But for How Long?

In an effort to transcend platform differences, the makers of Netscape and Microsoft's browsers and Mozilla put their heads together in late 1999 and decided to standardize on a default font size setting of 16px/96ppi across platforms. By putting all platforms on the same page, as it were, browser makers and users could avoid the problems of cross-platform size differences and cruelly useless, illegible text.

The 16px/96ppi Font Size Standard

On a W3C mailing list in 1998, the plucky Todd Fahrner puckishly proposed standardizing on a 16px default per Windows usage. His recommendation was adopted by all leading browser makers in the year 2000. Although Fahrner's concerns were practical in nature (he wanted to ensure that type could be read online), in the quotation that follows, he refers to something that might strike you as bizarre.

The framers of CSS were bound to a pet abstraction wherein the “average” length of a web user's arm was essential to defining the size of a pixel. No, really. Anyway, in advancing his idea about a standardized cross-platform font size, Fahrner was careful to cover the all-important arm length issue along with more pedestrian matters like usability. He wrote:

Since before Mosaic, the default font size value in all major browsers has been set at 12pt. I propose redefining the default as 16px…. The current default of 12pt rasterizes very differently across platforms. On Macs, it rasterizes into 12px (logical res fixed at 72ppi). On Wintel PCs, it rasterizes by default into 16px (logical res defaults to 96ppi). …All scalable font-size values… operate relative to this inconsistent base rasterization. For a designer, this means that the only way to suggest a [consistent cross-platform] font size is to use CSS pixel units, which are not user-scalable, and are thus not optimally user-friendly/ portable…

The appropriate corrective measure… is for Mac (and X11?) browsers to break with tradition and ship with the default value of “medium” text set at 16px, instead of 12pt. This should of course remain subject to user adjustment, but a consistent initial value will at least make the use of scalable font-size values less problematic for designers, as any variance from the default will be due to express user preference rather than capricious legacy OS differences.

If designers tend to believe that 16px is too large as a base, why suggest it as the default?

One reason is pure expediency. The Mac is a smallish minority platform, though very strongly represented in the web design field. (I use a Mac!) It is unrealistic to expect that Windows/X11 browsers will change their defaults to match the Mac's rather quaint limitation to 72ppi logical resolution.

The 1996 CSS1 standard suggests a 1/90” value for a “reference pixel,” extrapolated from a visual angle of 0.0227 degrees visual angle at arm's length. [User agents] are expected to scale pixels appropriately if the physical resolution is known to vary significantly from this value. A 1/90” reference pixel would suggest a rasterization of 12pt into 15px, rather than 16. 15 is, of course, much closer to 16 than to 12, however. Because no OS/UA currently assumes a 90ppi logical resolution (nor implements pixel-scaling) … the reference pixel value should be amended to 1/96”. It's simple to preserve the suggested 0.0227 degrees visual angle by giving the reference user a longer arm's length.

Designers think that 16px is too large simply because they are used to the 12px base size of their Macs. Readability is 9/10ths familiarity.


Two years later, the first generation of significantly standards-compliant browsers embraced Fahrner's recommendation. In Internet Explorer, Netscape, and Mozilla, on both the Windows and Macintosh platforms, the default text size became 16px/96ppi, and increased legibility was enjoyed throughout the globe (except when users quickly changed it back).

Fahrner's efforts eventually led the W3C to agree to a standard reference pixel size related to the 16px/96ppi concept, as seen in the CSS 2.1 working draft. In the excerpt that follows, you'll note that the W3C remains quite concerned about the average length of a reader's arm. We should be grateful they're only talking about the length of an arm:

It is recommended that the reference pixel be the visual angle of one pixel on a device with a pixel density of 96dpi and a distance from the reader of an arm's length. For a nominal arm's length of 28 inches, the visual angle is therefore about 0.0213 degrees. —CSS 2.1 Working Draft, http://www.w3.org/TR/CSS21/syndata.html#length-units

While the standard reference pixel would seem to clear the way for a W3C standard user default size, the two are not officially related. The W3C has spoken to the first issue, but not to the second.



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