Non-standard: This feature is non-standard and is not on a standards track. Do not use it on production sites facing the Web: it will not work for every user. There may also be large incompatibilities between implementations and the behavior may change in the future.

Deprecated: This feature is no longer recommended. Though some browsers might still support it, it may have already been removed from the relevant web standards, may be in the process of being dropped, or may only be kept for compatibility purposes. Avoid using it, and update existing code if possible; see the compatibility table at the bottom of this page to guide your decision. Be aware that this feature may cease to work at any time.

Warning: This is a property of the original CSS flexible box layout Module draft. It has been replaced in the specification. See flexbox for information about the current standard.

The box-flex-group CSS property assigns the flexbox's child elements to a flex group.

For flexible elements assigned to flex groups, the first flex group is 1 and higher values specify subsequent flex groups. The initial value is 1. When dividing up the box's extra space, the browser first considers all elements within the first flex group. Each element within that group is given extra space based on the ratio of that element's flexibility compared to the flexibility of other elements within the same flex group. If the space of all flexible children within the group has been increased to the maximum, the process repeats for the children within the next flex group, using any space left over from the previous flex group. Once there are no more flex groups, and there is still space remaining, the extra space is divided within the containing box according to the box-pack property.

If the box would overflow after the preferred space of the children has been computed, then space is removed from flexible elements in a manner similar to that used when adding extra space. Each flex group is examined in turn and space is removed according to the ratio of the flexibility of each element. Elements do not shrink below their minimum widths.


/* <integer> values */
box-flex-group: 1;
box-flex-group: 5;

/* Global values */
box-flex-group: inherit;
box-flex-group: initial;
box-flex-group: unset;

The box-flex-group property is specified as any positive <integer>.

Formal definition

Initial value1
Applies toin-flow children of box elements
Computed valueas specified
Animation typediscrete

Formal syntax

box-flex-group =


Simple usage example

In the original flexbox spec, box-flex-group could be used to assign flex children to different groups to distribute flexible space between:

article:nth-child(1) {
  -webkit-box-flex-group: 1;

article:nth-child(2) {
  -webkit-box-flex-group: 2;

This was only ever supported in WebKit-based browsers, with a prefix, and in subsequent versions of the spec this functionality does not have an equivalent. Instead, distribution of space inside the flex container is now handled using flex-basis, flex-grow, and flex-shrink.


Not part of any standard.

Browser compatibility

BCD tables only load in the browser

See also