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.

Try it

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

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

min-block-size: 20px;
writing-mode: horizontal-tb;

min-block-size: 15em;
writing-mode: vertical-lr;

<section class="default-example" id="default-example">
  <div class="transition-all" id="example-element">
    This is a box where you can change the minimum block size. <br />If there is
    more content than the minimum the box will grow in the block dimension as
    needed by the content.
  </div>
</section>

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

Syntax

/* <length> values */
min-block-size: 100px;
min-block-size: 5em;
min-block-size: anchor-size(self-inline);

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

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

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

Values

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

Formal definition

Formal syntax

min-block-size = 
  <'min-width'>  

<min-width> = 
  auto                                      |
  <length-percentage [0,∞]>                 |
  min-content                               |
  max-content                               |
  fit-content( <length-percentage [0,∞]> )  |
  <calc-size()>                             |
  <anchor-size()>                           

<length-percentage> = 
  <length>      |
  <percentage>  

<calc-size()> = 
  calc-size( <calc-size-basis> , <calc-sum> )  

<anchor-size()> = 
  anchor-size( [ <anchor-name> || <anchor-size> ]? , <length-percentage>? )  

<calc-size-basis> = 
  <size-keyword>  |
  <calc-size()>   |
  any             |
  <calc-sum>      

<calc-sum> = 
  <calc-product> [ [ '+' | '-' ] <calc-product> ]*  

<anchor-name> = 
  <dashed-ident>  

<anchor-size> = 
  width        |
  height       |
  block        |
  inline       |
  self-block   |
  self-inline  

<calc-product> = 
  <calc-value> [ [ '*' | / ] <calc-value> ]*  

<calc-value> = 
  <number>        |
  <dimension>     |
  <percentage>    |
  <calc-keyword>  |
  ( <calc-sum> )  

<calc-keyword> = 
  e          |
  pi         |
  infinity   |
  -infinity  |
  NaN        

Examples

Setting minimum block size for vertical text

HTML

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

CSS

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

Result

Specifications

Browser compatibility

See also

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