The flex CSS property specifies how a flex item will grow or shrink so as to fit the space available in its flex container. This is a shorthand property that sets flex-grow, flex-shrink, and flex-basis.

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:

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".
initial
This is the default value. 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".
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".
<positive-number>
The item is given the specified proportion of the free space in the container. This is equivalent to setting "flex: <positive-number> 1 0".

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

Syntax

/* Basic values */
flex: auto;
flex: initial;
flex: none;
flex: 2;

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

/* One value, width/height: flex-basis */
flex: 10em;
flex: 30px;

/* 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:

Two-value syntax: the first value must be a unitless <number> and it is interpreted as <flex-grow>. The second value must be one of:

Three-value syntax:

Values

<'flex-grow'>
Defines the flex-grow of the flex item. See <number> for more details. Negative values are considered invalid. Defaults to 1 when omitted.
<'flex-shrink'>
Defines the flex-shrink of the flex item. See <number> for more details. Negative values are considered invalid. Defaults to 1 when omitted.
<'flex-basis'>
Defines the flex-basis of the flex item. Any value valid for width and height properties are accepted. A preferred size of 0 must have a unit to avoid being interpreted as a flexibility. Defaults to 0 when omitted.
none
This keyword computes to 0 0 auto.

When using one or two unitless values, flex-basis changes from auto to 0. More information can be found in the draft for the Flexible Box Layout Module.

Formal syntax

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

Example

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

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

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

Result

Specifications

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

Initial valueas each of the properties of the shorthand:
Applies toflex items, including in-flow pseudo-elements
Inheritedno
Mediavisual
Computed valueas each of the properties of the shorthand:
Animation typeas each of the properties of the shorthand:
Canonical orderorder of appearance in the formal grammar of the values

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic supportChrome Full support 29
Full support 29
Full support 21
Prefixed
Prefixed Requires the vendor prefix: -webkit-
Edge Full support 12
Full support 12
Full support 12
Prefixed
Prefixed Requires 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.
No support 20 — 61
Notes
Notes Flex items that are sized according to their content are sized using fit-content, not max-content.
Full support 49
Prefixed
Prefixed Requires the vendor prefix: -webkit-
Full support 44
Prefixed Disabled
Prefixed Requires the vendor prefix: -webkit-
Disabled From version 44: this feature is behind the layout.css.prefixes.webkit preference (needs to be set to true). To change preferences in Firefox, visit about:config.
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.
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 Requires 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 12.1Safari Full support 9
Full support 9
Full support 6.1
Prefixed
Prefixed Requires the vendor prefix: -webkit-
WebView Android Full support 4.4
Full support 4.4
Full support Yes
Prefixed
Prefixed Requires the vendor prefix: -webkit-
Chrome Android Full support 29
Full support 29
Full support 25
Prefixed
Prefixed Requires the vendor prefix: -webkit-
Edge Mobile Full support Yes
Full support Yes
Full support Yes
Prefixed
Prefixed Requires the vendor prefix: -webkit-
Firefox Android ? Opera Android Full support 12.1Safari iOS Full support Yes
Full support Yes
Full support 7.1
Prefixed
Prefixed Requires the vendor prefix: -webkit-
Samsung Internet Android ?

Legend

Full support  
Full support
Compatibility unknown  
Compatibility unknown
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.

See also