block-size

The block-size CSS property defines the horizontal or vertical size of an element's block, depending on its writing mode. It corresponds to either the width or the height property, depending on the value of 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. A related property is inline-size, which defines the other dimension of the element.

Try it

Syntax

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

/* <percentage> 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 valueauto
Applies tosame as width and height
Inheritedno
Percentagesblock-size of containing block
Computed valuesame as width and height
Animation typea length, percentage or calc();

Formal syntax

block-size = 
  <'width'>

Examples

Block size with vertical text

HTML

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

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

Browser compatibility

Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
block-size
fit-content
fit-content()
Experimental
max-content
min-content

See also