Measure
In typography, measure is the width of a text column — how many characters fit on one line. On the web, it is controlled by max-width on the text container, often expressed in ch units.
Why it matters
Line length is the most common web typography mistake. Lines wider than 75 characters increase return-saccade errors; lines narrower than 45 break reading rhythm. Measure is a property of the text block, not the page wrapper.