auto

The width CSS property sets an element's width. By default it sets the width of the content area, but if box-sizing is set to border-box, it sets the width of the border area.

The min-width and max-width properties override width.

Syntax

/* <length> values */
width: 300px;
width: 25em;

/* <percentage> value */
width: 75%;

/* Keyword values */
width: 25em border-box;
width: 75% content-box;
width: max-content;
width: min-content;
width: available;
width: fit-content;
width: auto;

/* Global values */
width: inherit;
width: initial;
width: unset;

The width property is specified as either:

• one of the following keyword values: available, min-content, max-content, fit-content, auto.
• a <length> or a <percentage>. This may optionally be followed by one of the following keywords: border-box, content-box.

Values

<length>

Defines the width as an absolute value.

<percentage>

Defines the width as a percentage of the containing block's width. If the width of the containing block depends on the width of the element, the resulting layout is undefined.

border-box

If present, the preceding <length> or <percentage> is applied to the element's border box.

content-box

If present, the preceding <length> or <percentage> is applied to the element's content box.

auto

The browser will calculate and select a width for the specified element.

fill

Use the fill-available inline size or fill-available block size, as appropriate to the writing mode.

max-content

The intrinsic preferred width.

min-content

The intrinsic minimum width.

available

The containing block width minus horizontal margin, border and padding.

fit-content

The larger of:

• the intrinsic minimum width
• the smaller of the intrinsic preferred width and the available width

Formal syntax

[ <length> | <percentage> ] && [ border-box | content-box ]? | available | min-content | max-content | fit-content | auto

Examples

Default width

p.goldie {
  background: gold;
}

<p class="goldie">The Mozilla community produces a lot of great software.</p>

Pixels and ems

.px_length {
  width: 200px;
  background-color: red;
  color: white;
  border: 1px solid black;
}

.em_length {
  width: 20em;
  background-color: white;
  color: red;
  border: 1px solid black;
}

<div class="px_length">Width measured in px</div>
<div class="em_length">Width measured in em</div>

Percentage

.percent {
  width: 20%;
  background-color: silver;
  border: 1px solid red;
}

<div class="percent">Width in percentage</div>

max-content

p.maxgreen {
  background: lightgreen;
  width: intrinsic;           /* Safari/WebKit uses a non-standard name */
  width: -moz-max-content;    /* Firefox/Gecko */
  width: -webkit-max-content; /* Chrome */
}

<p class="maxgreen">The Mozilla community produces a lot of great software.</p>

min-content

p.minblue {
  background: lightblue;
  width: -moz-min-content;    /* Firefox */
  width: -webkit-min-content; /* Chrome */
}

<p class="minblue">The Mozilla community produces a lot of great software.</p>

Accessibility concerns

Ensure that elements set with a width are not truncated and do not obscure other content when the page is zoomed to increase text size.

• MDN Understanding WCAG, Guideline 1.4 explanations
• Understanding Success Criterion 1.4.4 | Understanding WCAG 2.0

Specifications

Browser compatibilityUpdate compatibility data on GitHub

See also

• box model, height, box-sizing, min-width, max-width