Column Width CPL

Comfortable column width & CPL (characters per line)

Few things move legibility as much as column width. Typographers measure it with CPL — Characters Per Line, the average count of glyphs (spaces included) that fit on one line of text. Robert Bringhurst, in The Elements of Typographic Style, puts the figure at 60–70 CPL for reading you do over a long stretch, and the wider band where things still feel comfortable runs from 50 to 75 characters.

To estimate the column width, use column-width ≈ CPL × 0.5em, which works because the average lowercase letter is about half an em wide. Drop below 45 CPL and the eye jumps too many times, chopping up comprehension. Go above 80 CPL and it struggles to find the start of the next line. Either way you end up reading more tired.

Applications

Web body text on long-form sites like Medium or Substack usually aims for 70–80 CPL. Printed books pull that in to 60–65 CPL, since paper handles denser type and fewer breaks well. Fiction genres like sci-fi and fantasy will often go down to 50–55 CPL with more leading, all in the name of immersion. ABNT NBR 14724, the Brazilian academic standard for theses and dissertations, asks for 60–80 CPL at 1.5 line spacing. Newspapers, going back decades, leaned on very narrow columns of 35–45 CPL so readers could skim quickly.

FAQ

How do I set this in CSS? Put max-width: 65ch; on your main content container. The ch unit matches the width of the “0” glyph in whatever font is active, so it gives you a CPL approximation that tracks the typeface.

Why is 66 chars/line considered ideal? Bringhurst points to it as the median across legibility studies going back to the 19th century. At that length the eye scans a line without losing the thread, and the brain finishes parsing it before the next jump.

Does CPL change with language? It does. Languages with longer average words, German and Portuguese among them, handle slightly wider columns; ones with shorter words, like English, sit comfortably toward the lower end of the range.