Line Height Calculator

How to use the line height calculator

1. Fill in the fields — they start with a worked example.
2. Read the answer, and the arithmetic shown beneath it.
3. Copy the results, or adjust the inputs to compare scenarios.

About this tool

Line height and line length are one decision, not two. A long line needs more space between lines, because the eye has further to travel back to find the start of the next one and a tight setting makes it land on the wrong line — the doubling and skipping that makes dense text tiring to read.

The measure — characters per line, counting spaces — is the variable that drives it. Between 45 and 75 characters is the range typography has settled on for continuous prose, with about 66 as the traditional ideal; below 45 the eye returns too often, above 75 it starts losing its place. This calculator takes the measure you want, gives the column width that produces it at your font size, and recommends a line height to match.

The recommendation is a convention rather than a law, and it is stated as one. It starts near 1.4 for a short measure and rises towards 1.7 for a long one, then tightens for large sizes: a 48-pixel headline at 1.5 looks like it has fallen apart, because leading that reads as generous at body size reads as a gap at display size.

Line height is given unitless, and that matters. `line-height: 1.5` is computed against each element's own font size, so a heading inside a container inherits the ratio rather than a fixed pixel value calculated from the parent — which is the bug behind headings whose lines overlap.

Common uses

• Setting body text that is comfortable to read at length.
• Finding the column width that gives a sensible measure.
• Tightening leading on large headings that look loose.

Frequently asked questions

What is a good line height for body text?

Around 1.5 for a typical measure, rising towards 1.7 for long lines and falling to about 1.15 for large headings. Longer lines need more space so the eye can find the next one.

How many characters should a line be?

Between 45 and 75 including spaces, with about 66 as the traditional ideal for continuous prose. Narrower makes the eye return too often; wider makes it lose its place.

Should line-height have a unit?

No. A unitless value is computed against each element's own font size, so nested elements inherit the ratio. A fixed pixel value inherits the number, which is how headings end up with overlapping lines.