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 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 value	auto
Applies to	same as width and height
Inherited	no
Percentages	block-size of containing block
Media	visual
Computed value	same as width and height
Animation type	discrete
Canonical order	the unique non-ambiguous order defined by the formal grammar

Syntax

/* <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;

Values

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

Formal syntax

<'width'>

Example

HTML Content

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

CSS Content

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

Specification

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

Browser compatibility

[1] Available since Gecko 38, but behind the preference layout.css.vertical-text.enabled, then disabled by default. The preference has been removed in Gecko 51 and this property cannot be disabled since this version.

See also

• The mapped physical properties: width and height
• writing-mode