flex

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

• a unitless <number>: then it is interpreted as <flex-grow>.
• a valid value for width: then it is interpreted as <flex-basis>.
• one of the keyword values none, auto, or initial.

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:

• a unitless <number>: then it is interpreted as <flex-shrink>.
• a valid value for width: then it is interpreted as <flex-basis>.

Three-value syntax:

• the first value must be a unitless <number> and it is interpreted as <flex-grow>.
• the second value must be a unitless <number> and it is interpreted as <flex-shrink>.
• the third value must be a valid value for width and is interpreted as <flex-basis>.

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.

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

Browser compatibilityUpdate compatibility data on GitHub

See also

• CSS Flexbox Guide: Basic Concepts of Flexbox
• CSS Flexbox Guide: Controlling Ratios of flex items along the main axis