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CSS3 flex-basis Property

Topic: CSS3 Properties ReferencePrev|Next


The flex-basis CSS property specifies the initial main size of the flex item.

The following table summarizes the usages context and the version history of this property.

Default value: auto
Applies to: Flex items
Inherited: No
Animatable: Yes. See animatable properties.
Version: New in CSS3


The syntax of the property is given with:

width | auto | initial | inherit

The example below shows the flex-basis property in action.

.flex-container {
    display: flex;      
.item1 {
    background: #ff80c0;
    -webkit-flex-basis: 300px; /* Safari 6.1+ */
    flex-basis: 300px;
.item2 {
    background: #8080ff;
    -webkit-flex-basis: 30%; /* Safari 6.1+ */
    flex-basis: 30%;
.item3 {
    width: 120px;

Property Values

The following table describes the values of this property.

Value Description
width A length in absolute or relative units that specifies the initial length of the flexible item. Negative values are invalid.
auto The width of the flexible item is equal to the value of it's width property. If the width property isn't specified for the flexible item, the width will be according to its content. This is default value.
initial Sets this property to its default value.
inherit If specified, the associated element takes the computed value of its parent element flex-basis property.

Browser Compatibility

The flex-basis property is supported in all major modern browsers.

Browsers Icon

Basic Support—

  • Firefox 18+ -moz-, 28
  • Google Chrome 21+ -webkit-, 29
  • Internet Explorer 10+ -ms-, 11
  • Apple Safari 6.1+ -webkit-
  • Opera 12.1+

Further Reading

See tutorial on: CSS3 Multi-column Layouts.

Related properties: align-content, align-items, align-self, display, flex, flex-direction, flex-flow, flex-grow, flex-shrink, flex-wrap, justify-content, min-height, min-width, order.

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