Web/CSS/flex

The flex CSS shorthand property sets how a flex item will grow or shrink to fit the space available in its flex container.

Constituent properties

This property is a shorthand for the following CSS properties:

Syntax

/* Keyword values */
flex: auto;
flex: initial;
flex: none;

/* One value, unitless number: flex-grow */
flex: 2;

/* One value, width/height: flex-basis */
flex: 10em;
flex: 30%;
flex: min-content;

/* Two values: flex-grow | flex-basis */
flex: 1 30px;

/* Two values: flex-grow | flex-shrink */
flex: 2 2;

/* Three values: flex-grow | flex-shrink | flex-basis */
flex: 2 2 10%;

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

The flex property may be specified using one, two, or three values.

One-value syntax: the value must be one of:
- a <number>: In this case it is interpreted as flex: <number> 1 0; the <flex-shrink> value is assumed to be 1 and the <flex-basis> value is assumed to be 0.
- one of the keywords: none, auto, or initial.
Two-value syntax:
- The first value must be:
  - a <number> and it is interpreted as <flex-grow>.
- The second value must be one of:
  - a <number>: then it is interpreted as <flex-shrink>.
  - a valid value for width: then it is interpreted as <flex-basis>.
Three-value syntax: the values must be in the following order:
1. a <number> for <flex-grow>.
2. a <number> for <flex-shrink>.
3. a valid value for width for <flex-basis>.

Values

initial: The item is sized according to its width and height properties. It shrinks to its minimum size to fit the container, but does not grow to absorb any extra free space in the flex container. This is equivalent to setting "flex: 0 1 auto".
auto: The item is sized according to its width and height properties, but grows to absorb any extra free space in the flex container, and shrinks to its minimum size to fit the container. This is equivalent to setting "flex: 1 1 auto".
none: The item is sized according to its width and height properties. It is fully inflexible: it neither shrinks nor grows in relation to the flex container. This is equivalent to setting "flex: 0 0 auto".
<'flex-grow'>: Defines the flex-grow of the flex item. Negative values are considered invalid. Defaults to 1 when omitted. (initial is 0)
<'flex-shrink'>: Defines the flex-shrink of the flex item. Negative values are considered invalid. Defaults to 1 when omitted. (initial is 1)
<'flex-basis'>: Defines the flex-basis of the flex item. A preferred size of 0 must have a unit to avoid being interpreted as a flexibility. Defaults to 0 when omitted. (initial is auto)

Description

For most purposes, authors should set flex to one of the following values: auto, initial, none, or a positive unitless number. To see the effect of these values, try resizing the flex containers below:

<div class="flex-container">
  <div class="item auto">auto</div>
  <div class="item auto">auto</div>
  <div class="item auto">auto</div>
</div>

<div class="flex-container">
  <div class="item auto">auto</div>
  <div class="item initial">initial</div>
  <div class="item initial">initial</div>
</div>

<div class="flex-container">
  <div class="item auto">auto</div>
  <div class="item auto">auto</div>
  <div class="item none">none</div>
</div>

<div class="flex-container">
  <div class="item initial">initial</div>
  <div class="item none">none</div>
  <div class="item none">none</div>
</div>

<div class="flex-container">
  <div class="item four">4</div>
  <div class="item two">2</div>
  <div class="item one">1</div>
</div>

* {
  box-sizing: border-box;
}

.flex-container {
  background-color: #F4F7F8;
  resize: horizontal;
  overflow: hidden;
  display: flex;
  margin: 1em;
}

.item {
  margin: 1em;
  padding: 0.5em;
  width: 110px;
  min-width: 0;
  background-color: #1B5385;
  color: white;
  font-family: monospace;
  font-size: 13px;
}

.initial {
  flex: initial;
}

.auto {
  flex: auto;
}

.none {
  flex: none;
}

.four {
  flex: 4;
}

.two {
  flex: 2;
}

.one {
  flex: 1;
}

By default flex items don't shrink below their minimum content size. To change this, set the item's min-width or min-height.

Formal definition

Initial value	as each of the properties of the shorthand: `flex-grow`: `0` `flex-shrink`: `1` `flex-basis`: `auto`
Applies to	flex items, including in-flow pseudo-elements
Inherited	no
Computed value	as each of the properties of the shorthand: `flex-grow`: as specified `flex-shrink`: as specified `flex-basis`: as specified, but with relative lengths converted into absolute lengths
Animation type	as each of the properties of the shorthand: `flex-grow`: a number `flex-shrink`: a number `flex-basis`: a length, percentage or calc();

Formal syntax

none | [ <'flex-grow'> <'flex-shrink'>? || <'flex-basis'> ]

Examples

Setting flex: auto

HTML

<div id="flex-container">
  <div class="flex-item" id="flex">Flex box (click to toggle raw box)</div>
  <div class="raw-item" id="raw">Raw box</div>
</div>

CSS

#flex-container {
  display: flex;
  flex-direction: row;
}

#flex-container > .flex-item {
  flex: auto;
}

#flex-container > .raw-item {
  width: 5rem;
}

var flex = document.getElementById("flex");
var raw = document.getElementById("raw");
flex.addEventListener("click", function() {
  raw.style.display = raw.style.display == "none" ? "block" : "none";
});

#flex-container {
  width: 100%;
  font-family: Consolas, Arial, sans-serif;
}

#flex-container > div {
  border: 1px solid #f00;
  padding: 1rem;
}

#flex-container > .raw-item {
  border: 1px solid #000;
}

Result

Specifications

Specification	Status	Comment
CSS Flexible Box Layout ModuleThe definition of 'flex' in that specification.	Candidate Recommendation	Initial definition

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`flex`	Chrome Full support 29 Full support 29 Full support 21 Prefixed' Prefixed' Implemented with the vendor prefix: -webkit-	Edge Full support 12 Full support 12 Full support 12 Prefixed' Prefixed' Implemented with the vendor prefix: -webkit-	Firefox Full support 20 Notes' Full support 20 Notes' Notes' Since Firefox 28, multi-line flexbox is supported. Notes' Before Firefox 32, Firefox wasn't able to animate values starting or stopping at `0`. Notes' Until Firefox 61, flex items that are sized according to their content are sized using `fit-content`, not `max-content`. No support 18 — 28 Disabled' Disabled' From version 18 until version 28 (exclusive): this feature is behind the `layout.css.flexbox.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. Full support 49 Prefixed' Prefixed' Implemented with the vendor prefix: -webkit- Full support 48 Prefixed' Disabled' Prefixed' Implemented with the vendor prefix: -webkit- Disabled' From version 48: this feature is behind the `layout.css.prefixes.webkit` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	IE Full support 11 Notes' Full support 11 Notes' Notes' Internet Explorer 11 ignores uses of `calc()` in the `flex-basis` part of the `flex` syntax. This can be worked around by using the longhand properties instead of the shorthand. See Flexbug #8 for more info. Notes' Internet Explorer 11 considers a unitless value in the `flex-basis` part to be syntactically invalid (and will thus be ignored). A workaround is to always include a unit in the `flex-basis` part of the `flex` shorthand value. See Flexbug #4 for more info. Full support 10 Prefixed' Notes' Prefixed' Implemented with the vendor prefix: -ms- Notes' Internet Explorer 10 and 11 ignore uses of `calc()` in the `flex-basis` part of the `flex` syntax. This can be worked around by using the longhand properties instead of the shorthand. See Flexbug #8 for more info. Notes' Internet Explorer 10 and 11 consider a unitless value in the `flex-basis` part to be syntactically invalid (and will thus be ignored). A workaround is to always include a unit in the `flex-basis` part of the `flex` shorthand value. See Flexbug #4 for more info.	Opera Full support 12.1	Safari Full support 9 Full support 9 Full support 6.1 Prefixed' Prefixed' Implemented with the vendor prefix: -webkit-	WebView Android Full support 4.4 Full support 4.4 Full support ≤37 Prefixed' Prefixed' Implemented with the vendor prefix: -webkit-	Chrome Android Full support 29 Full support 29 Full support 25 Prefixed' Prefixed' Implemented with the vendor prefix: -webkit-	Firefox Android Full support 20 Notes' Full support 20 Notes' Notes' Since Firefox 28, multi-line flexbox is supported. Notes' Before Firefox 32, Firefox wasn't able to animate values starting or stopping at `0`. Notes' Until Firefox 61, flex items that are sized according to their content are sized using fit-content, not max-content. No support 18 — 28 Disabled' Disabled' From version 18 until version 28 (exclusive): this feature is behind the `layout.css.flexbox.enabled` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config. Full support 49 Prefixed' Prefixed' Implemented with the vendor prefix: -webkit- Full support 48 Prefixed' Disabled' Prefixed' Implemented with the vendor prefix: -webkit- Disabled' From version 48: this feature is behind the `layout.css.prefixes.webkit` preference (needs to be set to `true`). To change preferences in Firefox, visit about:config.	Opera Android Full support 12.1	Safari iOS Full support 9 Full support 9 Full support 7 Prefixed' Prefixed' Implemented with the vendor prefix: -webkit-	Samsung Internet Android Full support 2.0 Full support 2.0 Full support 1.5 Prefixed' Prefixed' Implemented with the vendor prefix: -webkit-

Legend

Full support: Full support
See implementation notes.': See implementation notes.
User must explicitly enable this feature.': User must explicitly enable this feature.
Requires a vendor prefix or different name for use.': Requires a vendor prefix or different name for use.