line-height

The line-height CSS property sets the height of a line box in horizontal writing modes. In vertical writing modes, it sets the width of a line box. It's commonly used to set the distance between lines of text. On block-level elements in horizontal writing modes, it specifies the preferred height of line boxes within the element, and on non-replaced inline elements, it specifies the height that is used to calculate line box height.

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Syntax

css
/* Keyword value */
line-height: normal;

/* Unitless values: use this number multiplied
by the element's font size */
line-height: 3.5;

/* <length> values */
line-height: 3em;

/* <percentage> values */
line-height: 34%;

/* Global values */
line-height: inherit;
line-height: initial;
line-height: revert;
line-height: revert-layer;
line-height: unset;

The line-height property is specified as any one of the following:

  • a <number>
  • a <length>
  • a <percentage>
  • the keyword normal.

Values

normal

Depends on the user agent. Desktop browsers (including Firefox) use a default value of roughly 1.2, depending on the element's font-family.

<number> (unitless)

The used value is this unitless <number> multiplied by the element's own font size. The computed value is the same as the specified <number>. In most cases, this is the preferred way to set line-height and avoid unexpected results due to inheritance.

<length>

The specified <length> is used in the calculation of the line box height. Values given in em units may produce unexpected results (see example below).

<percentage>

Relative to the font size of the element itself. The computed value is this <percentage> multiplied by the element's computed font size. Percentage values may produce unexpected results (see the second example below).

Accessibility

Use a minimum value of 1.5 for line-height for main paragraph content. This will help people experiencing low vision conditions, as well as people with cognitive concerns such as Dyslexia. If the page is zoomed to increase the text size, using a unitless value ensures that the line height will scale proportionately.

W3C Understanding WCAG 2.1

Formal definition

Initial valuenormal
Applies toall elements. It also applies to ::first-letter and ::first-line.
Inheritedyes
Percentagesrefer to the font size of the element itself
Computed valuefor percentage and length values, the absolute length, otherwise as specified
Animation typeeither number or length

Formal syntax

line-height = 
normal                     |
<number [0,∞]>             |
<length-percentage [0,∞]>  

<length-percentage> = 
<length>      |
<percentage>

Examples

Basic example

css
/* All rules below have the same resultant line height */

/* number/unitless */
div {
  line-height: 1.2;
  font-size: 10pt;
}

/* length */
div {
  line-height: 1.2em;
  font-size: 10pt;
}

/* percentage */
div {
  line-height: 120%;
  font-size: 10pt;
}

/* font shorthand */
div {
  font:
    10pt/1.2 Georgia,
    "Bitstream Charter",
    serif;
}

It is often more convenient to set line-height by using the font shorthand as shown above, but this requires the font-family property to be specified as well.

Prefer unitless numbers for line-height values

This example shows why it is better to use <number> values instead of <length> values. We will use two <div> elements. The first div, with the green border, uses a unitless line-height value. The second div, with the red border, uses a line-height value defined in ems.

HTML

html
<div class="box green">
  <h1>Avoid unexpected results by using unitless line-height.</h1>
  Length and percentage line-heights have poor inheritance behavior.
</div>

<div class="box red">
  <h1>Avoid unexpected results by using unitless line-height.</h1>
  Length and percentage line-heights have poor inheritance behavior
</div>

<!-- The first <h1> line-height is calculated from its own font-size   (30px × 1.1) = 33px -->
<!-- The second <h1> line-height results from the red div's font-size  (15px × 1.1) = 16.5px, probably not what you want -->

CSS

css
.green {
  line-height: 1.1;
  border: solid limegreen;
}

.red {
  line-height: 1.1em;
  border: solid red;
}

h1 {
  font-size: 30px;
}

.box {
  width: 18em;
  display: inline-block;
  vertical-align: top;
  font-size: 15px;
}

Result

Space between lines in vertical writing modes

The line-height property can be used to adjust space between vertical lines in vertical writing modes.

css
.haiku {
  border: 1px solid;
  margin-bottom: 1rem;
  padding: 0.5rem;
  background-color: wheat;

  writing-mode: vertical-rl;
}

.wide {
  line-height: 2;
}

Result

Specifications

Specification
CSS Inline Layout Module Level 3
# line-height-property

Browser compatibility

BCD tables only load in the browser

See also