Measure

Robert Bringhurst puts a single column of text at 45 to 75 characters and calls 66 satisfactory. The US Web Design System, which has to work across an enormous range of readers and devices, treats 45 to 90 as the working range and reserves around 66 for long-form reading. These are not the same claim: the first is a typographer’s judgement about comfort, the second is a systems team’s judgement about tolerance. They agree on the middle and disagree about how much rope you get at the edges.

Notice that both are counted in characters, not pixels or ems or column units. That is the important part. The eye does not read distance, it reads words, and the cost of a long line is paid at the moment the eye has to travel back to the left margin and find the start of the next one. That return sweep is the whole problem, and its difficulty scales with how many words the eye has to track past.

The ch unit is the advance width of the digit zero in the current font. Setting a column in ch means the measure holds as the type size changes, which is exactly what you want and is why the control above is calibrated in ch rather than in pixels. But ch is not a character count. In most proportional faces the average character is narrower than a zero, so a column set to 66ch usually sets around 70 to 75 actual characters per line. The readout beside the specimen counts the real ones, by walking the rendered text and grouping characters by which line they landed on.

This matters because a great deal of advice on the web says “set your measure to 66ch” as though it delivered Bringhurst’s 66 characters. It does not. It delivers something closer to the top of his range. If you want 66 characters you want roughly 60ch, and the only way to know for your own face is to count.

The rule that ties this lesson to the previous one: a longer measure demands more leading. When the line is long, the return sweep is long, and the eye needs a wider horizontal channel to land in reliably. Open the measure above past 75 and the specimen’s leading opens with it, because the setting would otherwise be dishonest — a wide column at tight leading is not a measure problem or a leading problem, it is one problem wearing two hats.

The practical consequence is that you cannot fix a too-wide column by reducing the type size. Smaller type in the same pixel width means more characters per line, not fewer. It makes the problem worse while feeling like a remedy, which is why it is the most common wrong fix in the discipline. Narrow the column, or open the leading, or both.