block-size

Baseline Widely available *

This feature is well established and works across many devices and browser versions. It’s been available across browsers since January 2020.

* Some parts of this feature may have varying levels of support.

The block-size CSS property defines the size of an element's block along the block axis. If the writing-mode is horizontal, it corresponds to the height; if the writing mode is vertical, it corresponds to the width. A related property is inline-size, which defines the other dimension of the element.

Try it

block-size: 150px;
writing-mode: horizontal-tb;

block-size: 150px;
writing-mode: vertical-rl;

block-size: auto;
writing-mode: horizontal-tb;

block-size: auto;
writing-mode: vertical-lr;


  
    This is a box where you can change the block-size.

#example-element {
  display: flex;
  flex-direction: column;
  background-color: #5b6dcd;
  justify-content: center;
  color: #ffffff;
}

Syntax

css

/*  values */
block-size: 300px;
block-size: 25em;
block-size: anchor-size(height);
block-size: calc(anchor-size(--myAnchor block) * 0.75);

/*  values */
block-size: 75%;

/* Keyword values */
block-size: max-content;
block-size: min-content;
block-size: fit-content;
block-size: fit-content(20em);
block-size: auto;

/* Global values */
block-size: inherit;
block-size: initial;
block-size: revert;
block-size: revert-layer;
block-size: unset;

Values

The block-size property takes the same values as the width and height properties.

Formal definition

Initial value	`auto`
Applies to	same as `width` and `height`
Inherited	no
Percentages	block-size of containing block
Computed value	same as `width` and `height`
Animation type	a length, percentage or calc();

Formal syntax

block-size = 
  <'width'>  

 = 
  auto                                      |
                   |
  min-content                               |
  max-content                               |
  fit-content(  )  |
                               |
                             

 = 
        |
    

 = 
  calc-size(  ,  )  

 = 
  anchor-size( [  ||  ]? , ? )  

 = 
    |
     |
  any             |
        

 = 
   [ [ '+' | '-' ]  ]*  

 = 
    

 = 
  width        |
  height       |
  block        |
  inline       |
  self-block   |
  self-inline  

 = 
   [ [ '*' | / ]  ]*  

 = 
          |
       |
      |
    |
  (  )  

 = 
  e          |
  pi         |
  infinity   |
  -infinity  |
  NaN

Examples

Block size with vertical text

HTML

html

Example text

CSS

css

.exampleText {
  writing-mode: vertical-rl;
  background-color: yellow;
  block-size: 200px;
}

Result

Specifications

Specification
CSS Logical Properties and Values Level 1 # dimension-properties
CSS Box Sizing Module Level 4 # sizing-values