The flex-basis
CSS property sets the initial main size of a flex item. It sets the size of the content box unless otherwise set with box-sizing
.
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Note: in case both flex-basis
(other than auto
) and width
(or height
in case of flex-direction: column
) are set for an element, flex-basis
has priority.
Syntax
/* Specify <'width'> */ flex-basis: 10em; flex-basis: 3px; flex-basis: auto; /* Intrinsic sizing keywords */ flex-basis: fill; flex-basis: max-content; flex-basis: min-content; flex-basis: fit-content; /* Automatically size based on the flex itemβs content */ flex-basis: content; /* Global values */ flex-basis: inherit; flex-basis: initial; flex-basis: unset;
The flex-basis
property is specified as either the keyword content
or a <'width'>
.
Values
<'width'>
- An absolute
<length>
, a<percentage>
of the parent flex container's main size property, or the keywordauto
. Negative values are invalid. Defaults toauto
. content
- Indicates automatic sizing, based on the flex itemβs content.
-
Note: This value was not present in the initial release of Flexible Box Layout, and thus some older implementations will not support it. The equivalent effect can be had by using
auto
together with a main size (width or height) ofauto
.History:
- Originally,
flex-basis:auto
meant "look at mywidth
orheight
property". - Then,
flex-basis:auto
was changed to mean automatic sizing, and "main-size" was introduced as the "look at mywidth
orheight
property" keyword. It was implemented in bug 1032922. - Then, that change was reverted in bug 1093316, so
auto
once again means "look at mywidth
orheight
property"; and a newcontent
keyword is being introduced to trigger automatic sizing. (bug 1105111 covers adding that keyword).
- Originally,
Formal definition
Initial value | auto |
---|---|
Applies to | flex items, including in-flow pseudo-elements |
Inherited | no |
Percentages | refer to the flex container's inner main size |
Computed value | as specified, but with relative lengths converted into absolute lengths |
Animation type | a length, percentage or calc(); |
Formal syntax
content | <'width'>
Examples
Setting flex item initial sizes
HTML
<ul class="container"> <li class="flex flex1">1: flex-basis test</li> <li class="flex flex2">2: flex-basis test</li> <li class="flex flex3">3: flex-basis test</li> <li class="flex flex4">4: flex-basis test</li> <li class="flex flex5">5: flex-basis test</li> </ul> <ul class="container"> <li class="flex flex6">6: flex-basis test</li> </ul>
CSS
.container { font-family: arial, sans-serif; margin: 0; padding: 0; list-style-type: none; display: flex; flex-wrap: wrap; } .flex { background: #6AB6D8; padding: 10px; margin-bottom: 50px; border: 3px solid #2E86BB; color: white; font-size: 14px; text-align: center; position: relative; } .flex:after { position: absolute; z-index: 1; left: 0; top: 100%; margin-top: 10px; width: 100%; color: #333; font-size: 12px; } .flex1 { flex-basis: auto; } .flex1:after { content: 'auto'; } .flex2 { flex-basis: max-content; } .flex2:after { content: 'max-content'; } .flex3 { flex-basis: min-content; } .flex3:after { content: 'min-content'; } .flex4 { flex-basis: fit-content; } .flex4:after { content: 'fit-content'; } .flex5 { flex-basis: content; } .flex5:after { content: 'content'; } .flex6 { flex-basis: fill; } .flex6:after { content: 'fill'; }
Results
Specifications
Specification | Status | Comment |
---|---|---|
CSS Flexible Box Layout Module The definition of 'flex-basis' in that specification. |
Candidate Recommendation | Initial definition |
Browser compatibility
The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.
Desktop | Mobile | |||||||||||
---|---|---|---|---|---|---|---|---|---|---|---|---|
flex-basis | Chrome
Full support
29
| Edge
Full support
12
| Firefox
Full support
22
| IE
Full support
11
| Opera
Full support
12.1
| Safari
Full support
9
| WebView Android
Full support
4.4
| Chrome Android
Full support
29
| Firefox Android
Full support
22
| Opera Android
Full support
12.1
| Safari iOS
Full support
9
| Samsung Internet Android
Full support
2.0
|
auto | Chrome Full support 22 | Edge Full support 12 | Firefox Full support 18 | IE Full support 11 | Opera Full support 12.1 | Safari
Full support
7
| WebView Android Full support β€37 | Chrome Android Full support 25 | Firefox Android Full support 18 | Opera Android Full support 12.1 | Safari iOS
Full support
7
| Samsung Internet Android Full support 1.5 |
content | Chrome No support No | Edge No support 12 — 79 | Firefox Full support 61 | IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Firefox Android Full support 61 | Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No |
max-content | Chrome No support No | Edge No support No | Firefox
Full support
66
| IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Firefox Android
Full support
66
| Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No |
min-content | Chrome No support No | Edge No support No | Firefox
Full support
66
| IE No support No | Opera No support No | Safari No support No | WebView Android No support No | Chrome Android No support No | Firefox Android
Full support
66
| Opera Android No support No | Safari iOS No support No | Samsung Internet Android No support No |
Legend
- Full support
- Full support
- No support
- No 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.
See also
- CSS Flexbox Guide: Basic Concepts of Flexbox
- CSS Flexbox Guide: Controlling Ratios of flex items along the main axis
width