baihaihui baihaihui - 1 month ago 10
CSS Question

The difference between flex:1 and flex-grow:1

In mdn

  • flex:1

means the same as

  • flex-grow:1

However, in fact it has different show in browser.

You can try it in this jsFiddle by changing the comment in css.

When I use
flex: 1
the element who's classname is
will be
but it won't happen when you use
flex-grow: 1

I don't understand why. Looking for some help. Thanks very much.

.flex-1 {
display: flex;
flex-direction: column;
height: 500px;
background: red;

.child-1 {
height: 50px;
background: blue;

.child-2 {
flex-grow: 1;
/* flex:1; */
background: green;

.test-container {
display: flex;
flex-direction: row;
background: white;
height: 100%;

<div class="flex-1">
<div class="child-1"></div>
<div class="child-2">
<div class="test-container"></div>

Answer Source


The flex property is a shorthand for setting:

  • flex-grow
  • flex-shrink
  • flex-basis

The flex: 1 rule is supposed to compute to this:

  • flex-grow: 1
  • flex-shrink: 1
  • flex-basis: 0

These values are defined in the spec. See section 7.1.1. Basic Values of flex

I say "supposed to compute" because, in IE11 and possibly other browsers, a unit of measure, such as px or %, is appended to the 0 value in flex-basis. This can make a difference (example).


The flex-grow property (which distributes free space in the container among flex items), when declared by itself, leaves flex-shrink and flex-basis at their initial values.

So when you set flex-grow: 1, the browser renders this:

The difference between flex: 1 and flex-grow: 1

Ultimately, the difference between flex: 1 and flex-grow: 1 is that the former sets flex-basis: 0, and the latter keeps the default flex-basis: auto.

For a complete explanation of the difference between flex-basis: 0 and flex-basis: auto see this post:

Your code example

The reason you're seeing a difference in your code is that flex-basis controls height in a column-direction container.

In Chrome, with flex-basis: auto, the height of the element is 450px (500px parent - 50px header). In other words, flex-grow is free to distribute the free space.

With flex-basis: 0, the height of the element is 0, and flex-grow has no free space to distribute.

The height: 100% on the child of the flex item is simply ignored because it isn't being applied properly, as explained in these posts:

In reading the posts above you'll also understand why your code renders differently in Firefox, Safari, Edge and IE.