line-height

Summary

On block level elements, the line-height property specifies the minimum height of line boxes within the element.

On non-replaced inline elements, line-height specifies the height that is used to calculate line box height. On replaced inline elements such as buttons or other input elements, line-height has no effect. [1]

Syntax

/* Keyword values */
line-height: normal;

/* Unitless: 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: unset;

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>

The used value is this unitless <number> multiplied by the element's font size. The computed value is the same as the specified <number>. In most cases this is the preferred way to set line-height with no unexpected results in case of inheritance.

<length>

The specified <length> is used in the calculation of the line box height. See <length> values for possible units.

<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 and em values may have unexpected results, see "Notes" section.

Formal syntax

normal | <number> | <length> | <percentage>

Examples

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

div { line-height: 1.2;   font-size: 10pt }   /* number */ 
div { line-height: 1.2em; font-size: 10pt }   /* length */ 
div { line-height: 120%;  font-size: 10pt }   /* percentage */
div { line-height: 12pt;  font-size: 10pt }   /* length */
div { font: 10pt/1.2  Georgia,"Bitstream Charter",serif }

Notes

• It is often more convenient to set line-height by using the font shortcut as stated in the "Examples" section above.

Prefer unitless numbers for line-height values

This example shows why it is better to prefer <number> values for line-height instead of a <length>.

We will use two <div> elements. The first, with the green border, will use a unitless line-height value. The second, with the red border, has a length line-height value.

.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;
}

The HTML, with our two boxes:

<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 -->

Result:

Specifications

Browser compatibility

[1] Neither Webkit nor Trident implement the correct behavior with replaced inline elements like buttons. In some cases line-height is allowed to have an effect on them. This is incorrect behavior relative to the specification.

See also

• font, font-size