CSS - block-size


HTML Content

<p class="exampleText">Example text</p>

CSS Content

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


/* <length> values */
block-size: 300px;
block-size: 25em;

/* <percentage> values */
block-size: 75%;

/* Keyword values */
block-size: 25em border-box;
block-size: 75% content-box;
block-size: max-content;
block-size: min-content;
block-size: available;
block-size: fit-content;
block-size: auto;

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


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

Formal syntax



The block-size CSS property defines the horizontal or vertical size of an element's block depending on its writing mode. It corresponds to the width or the height property depending on the value defined for writing-mode.

If the writing mode is vertically oriented, the value of block-size relates to the width of the element, otherwise it relates to the height of the element. It relates to inline-size, which defines the other dimension of the element.

Initial valueauto
Applies tosame as width and height
Percentagesblock-size of containing block
Computed valuesame as width and height
Canonical orderthe unique non-ambiguous order defined by the formal grammar

Browser Compatibility  

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support No support 41.0 (41.0)[1] No support No support No support
Feature Android Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support No support 41.0 (41.0)[1] No support No support No support

[1] Available since Gecko 38, but behind the preference layout.css.vertical-text.enabled, then disabled by default.

See Also  


Specification Status Comment
CSS Logical Properties Level 1
The definition of 'block-size' in that specification.
Editor's Draft Initial definition


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.