line-height: Unitless Ratios, Inherited Lengths, and Line Boxes

CSS Reference

line-height participates in line-box height. A unitless value such as 1.6 scales with each element’s own font size, including when that ratio is inherited by larger child text.

Syntax and value choices

Property	Initial value	Inherited	Main application conditions
`line-height`	normal	Yes	All elements; visible effects depend on the text, image, or box conditions below

Initial values are not necessarily the values assigned to HTML elements by the browser’s stylesheet. Inspect the actual result in developer tools’ Computed panel.

body { font-size: 1rem; line-height: 1.6; }
.heading { line-height: 1.3; }

Value or category	Behavior and choice
`normal`	Font- and browser-dependent normal height, not a guaranteed 1.2 multiplier.
`1.6`	A unitless ratio multiplied by the element’s font size.
`28px`	A fixed line-height length.
`160%`	A percentage of this element’s font size, with length-like inheritance.

For supported values and conditions, see MDN line-height.

Run the example and compare results

Save this complete code as css-reference-10639-example.html in UTF-8 and open it in a browser. Keep its demonstration styles in that file rather than pasting them into a site-wide stylesheet.

<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<meta name="viewport" content="width=device-width, initial-scale=1">
<title>line-height comparison example</title>
<style>
body { margin: 0; color: #20242b; background: #fff; font: 16px/1.7 "Malgun Gothic", sans-serif; }
#demo { padding: 24px; max-width: 820px; margin: auto; }
h1 { font-size: 22px; margin: 0 0 20px; }
.samples { display: flex; flex-wrap: wrap; gap: 24px; }
.label { margin: 0 0 8px; font-weight: 700; }
.target, .reference { width: 260px; font-size: 20px; border: 1px solid #718096; }
.target { line-height: 1.6; }
.reference { line-height: 1; }
</style>
</head>
<body>
<main id="demo">
<h1>line-height comparison</h1>
<section class="samples"><div class="a"><p class="label">line-height: 1.6</p><div class="target">Compare line-height values.<br>The second line has the same font size.<br>Inspect the third line.</div></div><div class="b"><p class="label">line-height: 1</p><div class="reference">Compare line-height values.<br>The second line has the same font size.<br>Inspect the third line.</div></div></section>
</main>
</body>
</html>

The first 20px sample has a 32px line-height value. The second uses 1, leaving less room between glyphs; exact glyph appearance depends on the font.

Ratios versus inherited lengths

A unitless number is inherited as a ratio. Lengths resolved from px, em, or percentages can remain the same inherited length even when a child’s font grows. This distinction matters in wrappers containing larger headings.

Line height is not paragraph spacing

Paragraph margins separately control gaps between paragraphs. Centering a control with a fixed line-height can break when its text wraps; use suitable flex or grid alignment instead. Test enlargement and the actual scripts used in the text.

Compare inherited ratios and lengths

Save this complete document as css-reference-10639-practice.html in UTF-8 and open it in a browser. Test it as a separate file rather than nesting it inside another example.

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Compare inherited ratios and lengths</title>
  <style>
    body { margin: 16px; color: #20242b; font: 16px/1.7 sans-serif; }
    main { max-width: 52rem; margin: auto; }
    h1 { font-size: 1.35rem; }
    .samples { display: flex; flex-wrap: wrap; gap: 24px; }
    .samples > * { max-width: 100%; min-width: 0; }
    :focus-visible { outline: 3px solid #005fcc; outline-offset: 3px; }
.parent { font-size:20px;background:#e6f2ff;padding:8px;margin-bottom:20px; } .ratio {line-height:1.6;} .fixed {line-height:32px;} .child {font-size:30px;}
  </style>
</head>
<body>
<main>
  <h1>Compare inherited ratios and lengths</h1>
<p>line-height: 1.6</p><div class="parent ratio">Parent: 20px<div class="child">Child: 30px</div></div><p>line-height: 32px</p><div class="parent fixed">Parent: 20px<div class="child">Child: 30px</div></div>
</main>
</body>
</html>

Both parents compute to 32px, but the ratio child computes to 48px and the fixed-length child to 32px. The inherited number is multiplied by the child’s own font size. Change only .child to 40px, expect 64 and 32px, then restore it. Other inline content can enlarge a line box; distinguish this computed value from total paragraph height.

For coordinated font sizing, line heights, and typeface choices, see CSS Fonts, Font Sizes, and Line Height. Related properties to compare alongside these conditions are font-size.

When the result is missing or unexpected

Inspect inherited fixed lengths when large child text overlaps.
Inspect paragraph margin separately when the lines fit but paragraph gaps are large.

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