February 24th, 2013
The size of type, of an individual letterform in a particular typeface, is measured from the top of the highest ascender to the bottom of the lowest descender. (Note: I originally had some kind of brain freeze and defined this incorrectly. But Michael Brady was kind enough to point this out to me in a LinkedIn group discussion.) But that doesn’t mean different typefaces fall the same way on a page. Some typefaces have larger x-heights (measured from baseline to the top of, say, a lowercase x. Others have longer or shorter ascenders and/or descenders. So there are definite differences in how much space characters in any particular type occupy in comparison to those same characters set in another typeface.
Leading, as indicated by the dotted horizontal lines in the example above, is measured from baseline to baseline. After type size, leading is perhaps the simplest way to exert control over the color of the page—i.e., how dense (light or dark) the page looks.
Rule of thumb says 120% of the type size is a usual leading. So if the type size is 10 point, rule of thumb calls for 12 point leading.
Too little leading—the term originates from strips of lead placed between lines of type when type was set by hand, in metal, during the pre-digital age—and the page will be crowded with type and have a dark look.
Notice how the above example appears blacker than the one above it, which looks grayish in comparison.
Too much leading, on the other hand, distracts the reader’s eye. Such text looks disjointed, and the lines no longer appear to be joined into paragraphs. The page looks lighter still than the previous lighter page.
My sense over the last few years has been to use more and more leading, pulling up way short from too much, but definitely stretching beyond 120% of type size. With the ITC New Baskerville type I’ve used for all my examples, I was able to stretch the leading to 16 point, over 131%. And yet I think it clearly is not too much.
Stretching limits, but not rupturing them, I believe, is a good way to create page designs that are attractive and original, but do not distract readers from the books they read.