The ability to read quickly and to understand what is being read depends on good typographic design reducing the effort required to comprehend the text. (It also requires good writing and copyediting, but that’s for another post.)
For readability, the choice of typeface, upper and lower case (U&lc), typesize, leading, line length, margins and paper colour and all need to be combined to produce readable copy.
For instance, most books are set using a serif font rather than sans-serif, because the serifs help the reader’s eye to rapidly scan along the lines of type on a page. This gives U&lc serif faces a high readability factor for longer passages of text.
Whilst sans-serif faces generally have a relatively low readability factor when set to longer line lengths, they have high readability factor on signage and when set in shorter line lengths. Sans-serif offers a sense of urgency, enabling the reader to scan quickly down the copy and assimilate information – a more appropriate reading experience for signs and magazines.
Common text type sizes tend to be between 9 and 12 point (depending on font) with leading set automatically by design software at around 120% of the typesize. This should always be adjusted by the designer with an appropriate amount of leading determined by the design. As a rule of thumb, for normal text, leading should be increased proportionally until around 14 point, when it should be decreased proportionally until around 18 point, after which it should be set solid (ie. 18/18pt). With larger type sizes and headlines, the leading should be further reduced to avoid creating too much space between lines.
In typesetting for legibility, the leading should never be less than the spacing between words, otherwise the readers eye is drawn down rather than across the page. However headline setting can often be set solid, or even to a minus value, without affecting readability. For longer measures, the leading might also be increased so it provides stronger definition to the line of text. As a rule of thumb, the longer the line, the greater the leading required.
In English, the line length normally contains between 50 and 80 characters for readability, resulting in an average of nine to 12 words per line. Scientific and technical papers, which are likely to contain longer words, tend to need a longer measure.
Finally, the margins around the type should allow enough white space to allow the reader’s eye to rest momentarily until it scans back to the start of the next line.
Note that glossy white paper, whilst great for images, makes text difficult to read.
So, so as long as you print on a matt paper stock, readability is governed by the designers ability to structure typeface, case, size, leading, line length and margins into a compelling design.
