typography
Measure (line length)
The width of a block of text, counted in characters per line – 50–75 characters is the readable range.
Lines that run too long make your eye lose its place on the way back to the left edge; lines too short make reading feel like stop-start traffic. The comfortable range for body text is about 50–75 characters per line including spaces (Baymard Institute’s synthesis of the classic typographic research; WCAG’s related guideline says 80 or fewer).
This is why well-designed sites don’t let paragraphs stretch across a wide monitor – the column stops growing even when the screen doesn’t. The paragraphs on this site are capped at 68 characters for exactly this reason.