The magazine of the Melbourne PC User Group The Importance Of X-Height - For the bookshelf Major Keary

Two typefaces printed at the same point size can fool a reader into thinking that one has a larger point size than the other. The illusion is a result of the x-height, which is the vertical measure of the lowercase x. Why x? Characters with rounded shapes (called 'bowls'), such as c, o, e), are always drawn larger than letters with flat upper and/or lower surfaces (for example, v, w, x, z. The reason is that, if lower-case letters with bowls were drawn to the same vertical dimension as x they would look smaller to the human eye.

James Felici describes x-height as "the typographical equivalent of hemline length . [it] trends up and down over time" [The Complete Manual Of Typography]. By choosing a typeface with a generous x-height it is possible to use a smaller font size while retaining, or even improving, legibility. Typefaces with a book designation (for example Century Schoolbook, Bookman, Caxton Book, and ITC Kabel Book) usually - but not always - have a large x-height.

There is a catch: larger x-height usually means fatter letters, thus offsetting a significant part of the space-saving advantage. In some instances large x-height fonts require more leading. These are factors that have to be considered when choosing a typeface.

The samples illustrate the considerable differences in the appearance of a 'standard' (Times-Roman) typeface and others with varying degrees of 'large x-height'.

Kabel is an interesting example of a typeface with two very different x-heights. Designed by Rudolph Koch in 1927-30, the series was redrawn by the International Typeface Corporation (ITC) in 1986. The copyright resides with Linotype-Hell AG, but both versions are distributed under licence by Adobe; the ITC version is also licensed by a number of other vendors, including Bitstream. Both have the same point size, but - as can be seen from the samples - there is an extraordinary difference in the x-height. The original version appears to have much more leading (inter-line spacing) than the ITC version, but that is the result of ITC Kabel having a smaller font bounding box. ITC Kabel also demonstrates the effect of tight letter spacing on legibility.

Some of the samples - such as Caxton - illustrate the need for increased leading for better legibility. Americana looks like an example of a large x-height that doesn't do much for legibility. However, it was designed for headings, not body text, and is included to show the 'fattening' effect of large x-height. All but two of the samples are set at 10-point with 12-point leading.

The sample at bottom-right is set in 11 point Times-Roman with 12-point leading; note the difference in character size vis-à-vis the 10-point Times-Roman example at top left. Conventionally the leading for 11 point body text is 13.2 points, but in this instance it has been reduced to 12 points (which is the normal leading for 10-point body text). The purpose of that is to provide a comparison with the BT News sample that has been set at 9 points with leading increased to 12 points for better legibility.

Leading is measured from baseline to baseline and is usually 120 per cent of the font size; thus, 10-point body text would be set with 12-point leading. There is not room to discuss the topic here, but too much or too little can affect legibility. The aim of this article is to draw attention to the benefit - both space-saving and
legibility - of typefaces with a generous x-height. However, as one can see, bigger is not necessarily better.

Large x-height is very useful where very small print is required, as the 6-point examples (below) show.

A caveat: The samples have come from various data processing bureaux and type setters, and have been scanned to a TIF image. They have been through a lot more typesetting/imaging processes than this, the text you are reading now, and may not look as crisp and clean as they should.