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.

Try it

width: 150px;

width: 20em;

width: 75%;

width: auto;

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box where you can change the width.
  </div>
</section>

#example-element {
  display: flex;
  flex-direction: column;
  background-color: #5b6dcd;
  height: 80%;
  justify-content: center;
  color: white;
}

The specified value of width applies to the content area so long as its value remains within the values defined by min-width and max-width.

• If the value for width is less than the value for min-width, then min-width overrides width.
• If the value for width is greater than the value for max-width, then max-width overrides width.

Syntax

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

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

/* Keyword values */
width: max-content;
width: min-content;
width: fit-content;
width: auto;
width: stretch;

/* function values */
width: fit-content(20em);
width: anchor-size(width);
width: anchor-size(--my-anchor inline, 120%);
width: calc-size(max-content, size / 2);

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

Values

<length>

Defines the width as a distance value.

<percentage>

Defines the width as a percentage of the containing block's width.

auto

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

max-content

The intrinsic preferred width.

min-content

The intrinsic minimum width.

fit-content

Use the available space, but not more than max-content, i.e., min(max-content, max(min-content, stretch)).

anchor-size()

Sets the width relative to a dimension of an anchor element. When defining the width of an anchor-positioned element, the first parameter defaults to the associated anchor's width. If applied to a non-anchor-positioned element, it sets the width to the fallback value. If no fallback is defined, the declaration is ignored.

calc-size()

Sets the width to a modified intrinsic size.

fit-content(<length-percentage>)

Uses the fit-content formula with the available space replaced by the specified argument, clamping the width according to the formula min(maximum size, max(minimum size, <length-percentage>)).

stretch

Sets the width of the element's margin box to the width of its containing block. It attempts to make the margin box fill the available space in the containing block, so in a way behaving similar to 100% but applying the resulting size to the margin box rather than the box determined by box-sizing.

Accessibility

Ensure that elements set with a width aren't truncated and/or don't 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 | W3C Understanding WCAG 2.0

Formal definition

Formal syntax

width = 
  auto             |
  <box-size>       |
  <anchor-size()>  

<box-size> = 
  <length-percentage [0,∞]>                 |
  stretch                                   |
  contain                                   |
  min-content                               |
  max-content                               |
  fit-content                               |
  stretch( <length-percentage [0,∞]> )      |
  fit-content( <length-percentage [0,∞]> )  |
  <calc-size()>                             

<anchor-size()> = 
  anchor-size( [ <anchor-name> || <anchor-size> ]? , <length-percentage>? )  

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

<calc-size()> = 
  calc-size( <calc-size-basis> , <calc-sum> )  

<anchor-name> = 
  <dashed-ident>  

<anchor-size> = 
  width        |
  height       |
  block        |
  inline       |
  self-block   |
  self-inline  

<calc-size-basis> = 
  <size-keyword>  |
  <calc-sum>      |
  <calc-size()>   |
  any             

<calc-sum> = 
  <calc-product> [ [ '+' | '-' ] <calc-product> ]*  

<calc-product> = 
  <calc-value> [ [ '*' | / ] <calc-value> ]*  

<calc-value> = 
  <number>        |
  <dimension>     |
  <percentage>    |
  <calc-keyword>  |
  ( <calc-sum> )  

<calc-keyword> = 
  e          |
  pi         |
  infinity   |
  -infinity  |
  NaN        

Examples

Default width

This example demonstrates basic usage and the default auto value.

HTML

We include two paragraphs; one with a class name.

<p>The MDN community writes really great documentation.</p>
<p class="has-width">The MDN community writes really great documentation.</p>

CSS

We make all paragraphs have a gold background, explicitly setting the second paragraph's width to auto.

p {
  background: gold;
}
p.has-width {
  width: auto;
}

Results

As width defaults to auto, both paragraphs are the same width.

Using length units

This example demonstrates length width values.

HTML

We include two <div> elements with some text.

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

CSS

The px_length element is set to 200px while the em_length element is set to be 20em wide. Both elements also have different background-color, color, and border values to enable differentiating between the two when rendered.

.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;
}

Results

The px_length element will always be 200px wide. The rendered width of the em_length element depends on the font size.

Using percentages

This example demonstrates using percentage values.

HTML

We include one <div> element with some text.

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

CSS

We set the width of the element to be 20% of the width of its parent container.

.percent {
  width: 20%;

  background-color: silver;
  border: 1px solid red;
}

Results

Using intrinsic sizes

This example compares max-content and min-content, and introduces calc-size.

HTML

We include three paragraphs with the same content; just their class names differ.

<p class="max-green">The MDN community writes really great documentation.</p>
<p class="min-blue">The MDN community writes really great documentation.</p>
<p class="min-pink">The MDN community writes really great documentation.</p>

CSS

We set one paragraph's width to max-content, the second to min-content, and the third to be twice the size of the min-content by using the calc-size() function. Each is given a different background-color and border-style to enable differentiating between the two.

p.max-green {
  width: max-content;

  background-color: lightgreen;
  border-style: dotted;
}

p.min-blue {
  width: min-content;

  background-color: lightblue;
  border-style: dashed;
}

p.min-pink {
  width: calc-size(min-content, size * 2);

  background-color: pink;
  border-style: solid;
}

@supports not (width: calc-size(min-content, size * 2)) {
  body::before {
    content: "Your browser doesn't support the calc-size() function yet.";
    background-color: wheat;
    display: block;
    text-align: center;
    padding: 1rem 0;
  }
}

Results

The max-content example is as wide as the text. The min-content example is as wide as the widest word. The calc-size() example is set to be twice as wide as the min-content.

Using the stretch keyword

This example demonstrates the stretch value within a flex container.

HTML

We include a parent container with two child elements.

<div class="parent">
  <div class="child">text</div>
  <div class="child stretch">stretch</div>
</div>

CSS

We use the display property to make the parent a flex container, and set the second child's width the stretch.

.parent {
  border: solid;
  margin: 1rem;
  display: flex;
}

.child {
  background: #00999999;
  margin: 1rem;
}

.stretch {
  width: stretch;
}

@supports not (width: stretch) {
  body::before {
    content: "Your browser doesn't support the stretch value yet.";
    background-color: wheat;
    display: block;
    text-align: center;
    padding: 1rem 0;
  }
}

Result

By default, flex items are as wide as their content. The stretch value makes the element as wide as the available space allows, with the element's margin box otherwise clamped to the width of its containing block.

Using the anchor-size() function

This example demonstrates using the anchor-size() function to define the width of an anchor-positioned element; we defined its width as a multiple of its anchor's height.

HTML

We specify two <div> elements: one anchor element and one infobox element that we'll position relative to the anchor.

<div class="anchor">⚓︎</div>

<div class="infobox">
  <p>Infobox.</p>
</div>

CSS

We declare the anchor <div> as an anchor element by giving it an anchor-name. The positioned element has its position property set to absolute, and is associated with the anchor element via its position-anchor property. We also set absolute height and width dimensions on the anchor and define the width of the anchor-positioned element to be the width of the anchor using the anchor-size() function as the value of the width property. As a bonus, we also use the anchor-size() function to define the infobox's left position, making the gap between the anchor and the infobox one quarter of the height of the anchor.

.anchor {
  anchor-name: --my-anchor;
  width: 120px;
  height: 60px;

  font-size: 2rem;
  background-color: lightpink;
  text-align: center;
  align-content: center;
  outline: 1px solid black;
}

.infobox {
  position-anchor: --my-anchor;
  position: absolute;
  position-area: right;
  width: anchor-size(width);

  left: calc( anchor-size(height) / 4 )

  align-content: center;
  color: darkblue;
  background-color: azure;
  outline: 1px solid #dddddd;
}

body {
  padding: 5em;
}

@supports not (width: anchor-size(width)) {
  body::before {
    content: "Your browser doesn't support the anchor-size() function value.";
    background-color: wheat;
    display: block;
    text-align: center;
    padding: 1rem 0;
  }
}

Results

Note how the infobox's width is always the same as the anchor element's width.

Specifications

Browser compatibility

See also

• height
• box-sizing
• min-width, max-width
• block-size, inline-size
• SVG width attribute
• Introduction to the CSS box model guide
• CSS box model module
• CSS anchor positioning module
• CSS values and units module