CSS flex-basis Property

The flex-basis property specifies the initial main size of the flexible item. When this property is not included, its value is set to 0%.

The flex-basis property is one of the CSS3 properties.

If there are no flexible items, the flex-basis property won't have any effect.

The flex-basis property will have a priority when both flex-basis with a value other than auto and width (or height in case of flex-direction with a value set to column) are set.

Initial Value auto
Applies to Flex items, including in-flow pseudo-elements.
Inherited No.
Animatable Yes. Items are animatable.
Version CSS3
DOM Syntax object.style.flexBasis = "100px";

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Syntax

flex-basis: number | auto | initial | inherit;

Example of the flex-basis property:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      .box {
        width: 300px;
        height: 80px;
        border: 1px solid #666;
        display: -webkit-flex; /* Safari */
        display: flex;
      }
      .box div {
        -webkit-flex-grow: 0; /* Safari 6.1+ */
        -webkit-flex-shrink: 0; /* Safari 6.1+ */
        -webkit-flex-basis: 40px; /* Safari 6.1+ */
        flex-grow: 0;
        flex-shrink: 0;
        flex-basis: 40px;
      }
      .box div:nth-of-type(2) {
        -webkit-flex-basis: 140px;  /* Safari 6.1+ */
        flex-basis: 140px;
      }
    </style>
  </head>
  <body>
    <h2>Flex-basis property example</h2>
    <div class="box">
      <div style="background-color: #eeeeee;">40px</div>
      <div style="background-color: #1c87c9;">140px</div>
      <div style="background-color: #8ebf42;">40px</div>
      <div style="background-color: #cccccc;">40px</div>
      <div style="background-color: #666666;">40px</div>
    </div>
  </body>
</html>

Result

Example of the flex-basis property with all the values:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      .box {
        height: 70px;
        display: flex;
      }
      .box div {
        flex-grow: 0;
        flex-shrink: 0;
        flex-basis: 60px;
        padding: 15px;
        /* For Safari 6.1 and above browsers */
        -webkit-flex-grow: 0;
        -webkit-flex-shrink: 0;
        -webkit-flex-basis: 60px;
      }
      .box div:first-child {
        background-color: #40c3da;
      }
      .box div:nth-of-type(2) {
        flex-basis: 40%;
        -webkit-flex-basis: 40%;
        background-color: lightgreen;
      }
      .box div:nth-of-type(3) {
        flex-basis: auto;
        -webkit-flex-basis: auto;
        background-color: yellow;
      }
      .box div:nth-of-type(4) {
        flex-basis: initial;
        -webkit-flex-basis: initial;
        background-color: orange;
      }
      .box div:nth-of-type(5) {
        flex-basis: inherit;
        -webkit-flex-basis: inherit;
        background-color: pink;
      }
    </style>
  </head>
  <body>
    <h2>Flex-basis property example</h2>
    <div class="box">
      <div>
        number 60px
      </div>
      <div>
        percentage 40%
      </div>
      <div>
        auto
      </div>
      <div>
        initial
      </div>
      <div>
        inherit
      </div>
    </div>
  </body>
</html>

Example of the flex-basis property specified in pixels:

<!DOCTYPE html>
<html>
  <head>
    <title>Title of the document</title>
    <style>
      .box {
        width: 460px;
        height: 70px;
        display: flex;
      }
      .box div {
        flex-grow: 0;
        flex-shrink: 0;
        flex-basis: 70px;
        padding: 15px;
        /* For Safari 6.1 and above browsers */
        -webkit-flex-grow: 0;
        -webkit-flex-shrink: 0;
        -webkit-flex-basis: 70px;
      }
      .box div:first-child {
        background-color: #40c3da;
      }
      .box div:nth-of-type(2) {
        flex-basis: 100px;
        -webkit-flex-basis: 100px;
        background-color: lightgreen;
      }
      .box div:nth-of-type(3) {
        background-color: #1c87c9;
      }
      .box div:nth-of-type(4) {
        flex-basis: 150px;
        -webkit-flex-basis: 150px;
        background-color: orange;
      }
      .box div:nth-of-type(5) {
        background-color: #8ebf42;
      }
    </style>
  </head>
  <body>
    <h2>Flex-basis property example</h2>
    <div class="box">
      <div>
        70px
      </div>
      <div>
        100px
      </div>
      <div>
        70px
      </div>
      <div>
        150px
      </div>
      <div>
        70px
      </div>
    </div>
  </body>
</html>

Values

Value Description Play it
number Specifies the length of the item by "auto", "inherit", or a number followed by "%", "px", "em" etc. Play it »
auto This value is the default value of this property. Length is equal the flexible item's length. If there is no specified item length, it will be according to its content. Play it »
initial Sets the property to its default value. Play it »
inherit Inherits this property from its parent element.

Browser support
29.0+
21-28 -webkit- 		28.0+ 9.0+
6.1-8.0 -webkit- 		12.1+

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