On tradition, harmony, pitch, the atonal, typography, Fibonacci, and coincidence.
Harmony and pitch.
In §3.1.1 of The Elements of Typographic Style, Robert Bringhurst draws an analogy between the sequence of type sizes traditionally used by typographers and the diatonic scale.
In the sixteenth century, a series of common sizes developed among European typographers, and the series survived with little change and few additions for 400 years. [...] This is the typographic equivalent of the diatonic scale. But modern equipment makes it possible to set, in addition to these sizes, all the sharps and flats and microtonal intervals between.
In other words, modern typesetting – done via software and printer, instead of type and press – allows the atonal. Unlike in music, however, alternate systems have not arisen.
Further, typesetting on the web makes it not just possible to avoid the traditional sizes, but actually difficult to set them. There are so many issues involved: Which browser is being used, what its defaults are, what units you use to specify sizes, the flow of inheritance of sizes through the page, etc. If you’ve done more than a dab of web design, you’re well familiar with how complex type sizing can be.
But what’s important here is not the precise size of each piece of text on your site, as rendered on the client by a browser. What matters is the size of each piece of text relative to the others.
To put it again in musical terms, the specific frequency of the note is less important than the overall structure of the scale containing that note. Harmony, not pitch. As if typesetting had returned to the days when one orchestra’s A was quite different from another’s.
The tradition.
Here’s a section of that traditional sequence, set for the web:
The traditional scale continues both above and below the sizes shown here. But this seems pretty much enough for the web. Much smaller, and the type is hard to read. Much bigger, and you’re dealing with a strange case.
Implementing this system is simple. Sticking to it rigorously, in the absence of any external constraints, is the hard part.
Implementation, in theory.
Following Richard Rutter’s text sizing method, I start by declaring the font-size of the document’s body:
body {
font-size: 100%;
}
This minimizes text size variation across browsers, especially in the extreme (large and small) sizes. 100% is, in theory, equal to 16px. User defaults and zooming can easily change that, even if nothing else does. But that’s okay: All I’m concerned with is the relative sizing of the type.
All the sites I’ve designed recently have had a wrapper div containing the entire contents of the page. Like so:
<body>
<div class="everything">
The whole damn page.
</div>
</body>
I can take advantage of that wrapper div to bring down the whole page’s font-size to 10px:
#everything {
font-size: 0.625em; /* 16px * 0.625 ≈ 10px, or long primer size. */
}
10px is great, both because it’s about the smallest size I care to use normally and because it simplifies the following math tremendously. All the visible contents of the page are contained within div#everything, so all the elements will inherit a computed font-size of 10px. So I can resize them in in terms of em, which is effectively a simple multiplier. To get 14px type all I have to do is multiply the inherited value by 1.4: font-size: 1.4em.
You might note that I’ve blurred the distinction between points and pixels. (Oh lord. Let’s not get into the whole pixel unit discussion.) And I’m talking about things in terms of pixels as if their sizes could be possibly be fixed. But again, neither matters here. What matters are the relationships between the numbers, not the actual numbers themselves. It’s a matter of harmony, not frequency.
You might further note that I’m not declaring the line-height of anything, nor discussing it at all. line-height is another story entirely, and one I’ll deal with separately.
At any rate, I can go on and declare the type sizes of some common elements based on the page-wide default of 10px I’ve set:
h1 {
font-size: 2.4em; /* 10px * 2.4 = 24px, or double pica size. */
}
h2 {
font-size: 2.1em; /* 10px * 2.1 = 21px, or double small pica size. */
}
p {
font-size: 1.2em; /* 10px * 1.2 = 12px, or pica size. */
}
Simple enough. Though, as I said above, the theory of the implementation is easy.
Systems.
This is not about blind adherence to tradition. A coherent, harmonious system is more likely to produce elegant and satisfying results than a haphazard jumble.
Other systems are, of course, possible. Bringhurst, in §8.2, suggests alternatives based on the Fibonacci sequence and the golden section, including two different double-stranded Fibonacci series, one used by Le Corbusier in his Modulor scale.
Those are intellectually satisfying, but their actual make-up seems less useful for typesetting on the web. The Modulor system uses fractional sizes, and browser sub-pixel rendering problems are ample enough in normal usage – no need to encourage them. And both sequences are lighter on sizes in the low end of the range, which seems the most useful part of it for web work.
The traditional sequence seems good enough for my purposes.
Coincidence.
Also note that today’s date, as written in the States, is 3-5-8, which makes today a sort of Fibonacci day.