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Line Length (Measure) Optimizer

Line length, called the measure in typography, is how many characters fit on one line of text, and it has an outsized effect on whether a page is comfortable to read. Typographers settled on roughly 50 to 75 characters per line for body text, with 66 as the classic target, and the WCAG accessibility guidelines cap readable Latin text at 80 characters. This tool turns that rule into a working number for your layout. Pick a typeface and font size, drag the characters-per-line slider, and read a live sample paragraph set to exactly that width, so you judge it with your eyes instead of guessing. It outputs the max-width three ways: in ch units (the CSS-native way to cap measure), in rem, and in approximate pixels. The pixel and rem figures come from measuring the average character width of your chosen font on a canvas, which is more accurate for real prose than relying on the width of a single zero. Edit the sample text to paste your own copy and the column re-flows instantly.

Ideal body text: 50-75. WCAG limit: 80 (Latin).

Quick presets

Recommended max-width

max-width: 66ch;

Live sample at this measure

Measured: ~66 chars/line

Tip: edit the paragraph above to test your own copy. The column width is fixed to your target measure so you can read it like a real layout.

How to Find Your Ideal Line Length

  1. Pick the typeface - Choose the font stack closest to your site's body font from the Typeface menu (serif, sans, or monospace).
  2. Set the font size - Drag the Font size slider to your actual body size (16 to 20px is typical for the web).
  3. Tune the measure - Drag the characters-per-line slider, or use the 45, 66, and 80 presets, while the zone label tells you whether you are below ideal, in range, or past the WCAG limit.
  4. Read the live sample - Check the editable paragraph set to that exact width, and paste your own copy to test real content.
  5. Copy the value - Copy max-width in ch, rem, or px and drop it onto your text container.

Why This Tool?

Search for line length and you mostly find articles explaining the 50 to 75 character rule, not a tool that turns it into CSS you can paste. That gap is the reason this exists. Knowing the rule is easy; setting a real column to it and seeing whether 66 characters actually feels right in your font is the part people skip, and it is exactly where readability is won or lost. Robert Bringhurst's Elements of Typographic Style and decades of eye-tracking research point to the same range because lines that are too long make the eye lose its place on the return sweep, while lines that are too short break the natural rhythm of reading.

The CSS ch unit is the right primitive for capping measure because it scales with the font, so max-width: 66ch stays sensible whether your text is 16px or 20px. This tool leads with ch for that reason, then provides rem and pixel equivalents for design handoffs and tools that do not think in characters. Because the pixel figure is derived by measuring the average advance width of letters in your selected typeface, it reflects how your actual prose sets rather than a worst-case glyph.

Pairing a sensible measure with comfortable line height (around 1.5 for body text) is one of the cheapest, highest-impact typography decisions you can make. It costs one CSS declaration and makes long-form content noticeably easier to read on phones and wide monitors alike.