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

If the writing mode is vertically oriented, the value of min-block-size relates to the minimum width of the element; otherwise, it relates to the minimum height of the element. A related property is min-inline-size, which defines the other dimension of the element.


/* <length> values */
min-block-size: 100px;
min-block-size: 5em;

/* <percentage> values */
min-block-size: 10%;

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

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


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

Formal definition

Initial value0
Applies tosame as width and height
Percentagesblock-size of containing block
Computed valuesame as min-width and min-height
Animation typea length, percentage or calc();

Formal syntax



Setting minimum block size for vertical text


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


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



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

Browser compatibility

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See also