max-block-size

The max-block-size CSS property specifies the maximum size of an element in the direction opposite that of the writing direction as specified by writing-mode. That is, if the writing direction is horizontal, then max-block-size is equivalent to max-height; if the writing direction is vertical, max-block-size is the same as max-width.

The other dimension's maximum length is specified using the max-inline-size property.

This is useful because the max-width is always used for horizontal sizes and max-height is always used for vertical sizes, and if you need to set lengths based on the size of your text content, you need to be able to do so with the writing direction in mind.

Any time you would normally use max-height or max-width, you should instead use max-block-size to set the maximum "height" of the content (even though this may not be a vertical value) and max-inline-size to set the maximum "width" of the content (although this may instead be vertical rather than horizontal). See the Example in writing-mode, which shows the different writing modes in action.

Syntax

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

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

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

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

Values

The max-block-size property's value can be any value that's legal for the max-width and max-height properties:

<length>: Defines the max-width as an absolute value.
<percentage>: Defines the max-width as a percentage of the containing block's width.
none: No limit on the size of the box.
max-content: The intrinsic preferred max-width.
min-content: The intrinsic minimum max-width.
fit-content(<length-percentage>): Uses the fit-content formula with the available space replaced by the specified argument, i.e. min(max-content, max(min-content, argument)).

How writing-mode affects directionality

The values of writing-mode affect the mapping of max-block-size to max-width or max-height as follows:

Values of `writing-mode`	`max-block-size` is equivalent to
`horizontal-tb`, `lr` , `lr-tb` , `rl` , `rb` , `rb-rl`	`max-height`
`vertical-rl`, `vertical-lr`, `sideways-rl` , `sideways-lr` , `tb` , `tb-rl`	`max-width`

Note: The writing-mode values sideways-lr and sideways-rl were removed from the CSS Writing Modes Level 3 specification late in its design process. They may be restored in Level 4.

Note: The writing modes lr, lr-tb, rl, rb, and rb-tl are no longer allowed in HTML contexts; they may only be used in SVG 1.x contexts.

Formal definition

Initial value	`0`
Applies to	same as `width` and `height`
Inherited	no
Percentages	block-size of containing block
Computed value	same as `max-width` and `max-height`
Animation type	a length, percentage or calc();

Formal syntax

<'max-width'>

Examples

Setting max-block-size with horizontal and vertical text

In this example, the same text (the opening sentences from Herman Melville's novel Moby-Dick) is presented in both the horizontal-tb and vertical-rl writing modes.

Everything else about the two boxes is identical, including the values used for max-block-size.

HTML

The HTML establishes the two <div> blocks that will be presented with their writing-mode set using the classes horizontal or vertical. Both boxes share the standard-box class, which establishes coloring, padding, and their respective values of max-block-size.

<p>Writing mode <code>horizontal-tb</code> (the default):</p>
<div class="standard-box horizontal">
  Call me Ishmael. Some years ago—never mind how
  long precisely—having little or no money in my
  purse, and nothing particular to interest me on
  shore, I thought I would sail about a little and see
  the watery part of the world. It is a way I have of
  driving off the spleen and regulating the
  circulation.
</div>

<p>Writing mode <code>vertical-rl</code>:</p>
<div class="standard-box vertical">
  Call me Ishmael. Some years ago—never mind how
  long precisely—having little or no money in my
  purse, and nothing particular to interest me on
  shore, I thought I would sail about a little and see
  the watery part of the world. It is a way I have of
  driving off the spleen and regulating the
  circulation.
</div>

CSS

The CSS defines three classes. The first, standard-box, is applied to both boxes, as seen above. It provides standard styling including the minimum and maximum block sizes, font size, and so forth.

After that come the classes horizontal and vertical, which add the writing-mode property to the box, with the value set to horizontal-tb or vertical-rl depending on which class is used.

.standard-box {
  padding: 4px;
  background-color: #abcdef;
  color: #000;
  font: 16px "Open Sans", "Helvetica", "Arial", sans-serif;
  max-block-size: 160px;
  min-block-size: 100px;
}

.horizontal {
  writing-mode: horizontal-tb;
}

.vertical {
  writing-mode: vertical-rl;
}

Result

Specifications

Specification
CSS Logical Properties and Values Level 1 (CSS Logical Properties 1) # propdef-max-block-size

Browser compatibility

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	WebView Android	Chrome Android	Firefox for Android	Opera Android	Safari on IOS	Samsung Internet
`max-block-size`	57	79	41	No	44	12.1	57	57	41	43	12.2	5.0
`fit-content`	57	79	No	No	44	12.1	57	57	No	43	12.2	5.0
`fit-content_function`	No	No	91	No	No	No	No	No	91	No	No	No
`max-content`	57	79	66 41	No	44	12.1	57	57	66 41	43	12.2	5.0
`min-content`	57	79	66 41	No	44	12.1	57	57	66 41	43	12.2	5.0