width

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;
width: anchor-size(width);
width: anchor-size(--my-anchor inline, 120%);

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

/* Keyword values */
width: max-content;
width: min-content;
width: fit-content;
width: fit-content(20em);
width: auto;
width: stretch;

/* 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)).

fit-content(<length-percentage>)

Uses the fit-content formula with the available space replaced by the specified argument, i.e., min(max-content, max(min-content, <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                                      |
  <length-percentage [0,∞]>                 |
  min-content                               |
  max-content                               |
  fit-content( <length-percentage [0,∞]> )  |
  <calc-size()>                             |
  <anchor-size()>                           |
  stretch                                   |
  fit-content                               |
  contain                                   

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

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

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

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

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

<anchor-name> = 
  <dashed-ident>  

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

<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

p.gold {
  background: gold;
}

<p class="gold">The MDN community writes really great documentation.</p>

Example using 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>

Example with percentage

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

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

Example using "max-content"

p.max-green {
  background: lightgreen;
  width: max-content;
}

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

Example using "min-content"

p.min-blue {
  background: lightblue;
  width: min-content;
}

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

Stretch width to fill the containing block

HTML

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

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

CSS

@supports not (width: stretch) {
  .parent {
    display: none !important;
  }

  body::after {
    content: "Your browser doesn't support the `stretch` value yet.";
  }
}

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

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

.stretch {
  width: stretch;
}

Result

Specifications

Browser compatibility

See also

• height
• box-sizing
• min-width, max-width
• block-size, inline-size
• anchor-size()
• SVG width attribute
• Introduction to the CSS box model guide
• CSS box model module