Measure

Measure is controlled in CSS through the max-width property on a text container. A common starting point is max-width: 65ch, where the ch unit represents the width of the 0 character in the current font. This targets approximately 65 characters per line, the upper end of the comfortable reading range. For body text, a measure between 45 and 75 characters per line is recommended for most Latin alphabets.

Making columns too wide. The most common measure mistake is thinking wide columns save vertical space. They do, but at the cost of readers having to make long eye movements across each line, which slows reading and increases fatigue.

Using fixed pixel widths instead of relative units. A column set to 800 px ignores the user's font size preference. Use ch units or a max-width percentage so the measure responds to user preferences.

The measure is the line length, and the reading research is consistent: body text between 45 and 75 characters per line keeps the eye's return trip short and the rhythm steady. Below 45 characters, lines break too often and text starts to look like a list; above 75, the eye loses its place on the next line and reading slows. A 65-character target is a safe default for web body copy.

In CSS the easiest control is a constrained width on the text block, often expressed in ch units so it tracks the size of the letterforms: a card that stretches to 70ch keeps a comfortable measure regardless of font size. Measure also feeds the other settings: wider lines want more line-height, and tighter leading feels fine on narrow columns. The type scale calculator and the fluid type generator both work from a base size you can tune against a realistic paragraph width.