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<pre class="metadata">
Title: CSS Multi-column Layout Module Level 1
Group: CSSWG
Shortname: css-multicol
Level: 1
Status: ED
Prepare for TR: no
Implementation Report: https://test.csswg.org/harness/results/css-multicol-1_dev/grouped/
Work Status: Testing
WPT Path Prefix: /css/css-multicol/
WPT Display: closed
ED: https://drafts.csswg.org/css-multicol/
TR: https://www.w3.org/TR/css-multicol-1/
Previous Version: https://www.w3.org/TR/2021/CR-css-multicol-1-20211012/
Previous Version: https://www.w3.org/TR/2021/WD-css-multicol-1-20210212/
Previous Version: https://www.w3.org/TR/2019/WD-css-multicol-1-20191015/
Previous Version: https://www.w3.org/TR/2018/WD-css-multicol-1-20180528/
Previous Version: https://www.w3.org/TR/2017/WD-css-multicol-1-20171005/
Previous Version: https://www.w3.org/TR/2011/CR-css3-multicol-20110412/
Previous Version: https://www.w3.org/TR/2009/CR-css3-multicol-20091217/
Previous Version: https://www.w3.org/TR/2009/WD-css3-multicol-20090630/
Previous Version: https://www.w3.org/TR/2007/WD-css3-multicol-20070606/
Previous Version: https://www.w3.org/TR/2005/WD-css3-multicol-20051215/
Previous Version: https://www.w3.org/TR/2001/WD-css3-multicol-20010118/
Previous Version: http://www.w3.org/1999/06/WD-css3-multicol-19990623
Editor: Florian Rivoal, On behalf of Bloomberg, https://florian.rivoal.net, w3cid 43241
Editor: Rachel Andrew, Google, rachelandrew@google.com, w3cid 81117
Former Editor: Håkon Wium Lie, Opera Software, howcome@opera.com, w3cid 9796
Issue Tracking: Disposition of Comments https://drafts.csswg.org/css-multicol-1/issues
Abstract: This specification describes multi-column layouts in CSS, a style sheet language for the web. Using functionality described in the specification, content can be flowed into multiple columns with a gap and a rule between them.
Link Defaults: css-color (property) color, css21 (property) max-height, css-backgrounds-3 (value) hidden
Include Can I Use Panels: yes
</pre>
<pre class="link-defaults">
spec:css-sizing-3; type:property; text:min-height
spec:css-break-4; type:dfn; text:fragment
spec:css-align-3; type:property; text:column-gap
spec:css-align-3; type:value; for:column-gap; text:normal
spec:css-display-3; type:property; text:display
</pre>
<style type="text/css">
.cols { width: 500px; height: 200px; background: #fff; position: relative; border: solid 5px blue; margin: 0.5em 2em 1em 0; font: bold 14px/19px Arial, sans-serif }
.cols p { padding: 3px; margin: 0 }
.col { position: absolute; left: 0px; top: 0; z-index: 6; width: 170px }
.gap { position: absolute; background: green; width: 5px; bottom: 0px; top: 0px; border: 10px solid yellow; border-top-width: 0; border-bottom-width: 0; }
.rep { position: absolute; top: 45px; background: black; height: 110px; width: 100px; color: white; z-index: 4 }
table.breaks { border-collapse: collapse; margin: 1em 0 }
table.breaks td, table.breaks th { border: thin solid black; padding: 0.1em 0.2em }
div.example:before { width: 9em }
</style>
<h2 id="introduction">
Introduction</h2>
(This section is not normative.)
This module describes <dfn export>multi-column layout</dfn> in CSS.
By using functionality described in this document,
style sheets can declare that the content of an element
is to be laid out in multiple columns.
Other layout methods in CSS,
when applied to a parent element,
change the display properties of the direct children.
For example if a three column grid layout is created,
the direct children of the [=grid container=] become [=grid items=]
and are placed into the column tracks,
one element per cell with additional rows created as needed.
The child elements of a [=multi-column container=] however continue in normal flow,
that flow is arranged into a number of columns.
These columns have a flexible inline size,
and therefore respond to available space
by changing the size or number of columns displayed.
Multi-column layouts are easy to describe in CSS.
Here is a simple example:
<div class=example>
<pre highlight="css">body { column-width: 12em }</pre>
In this example, the <code class=html>body</code> element is
set to have columns at least ''12em'' wide. The exact number of
columns will depend on the available space.
</div>
The number of columns can also be set explicitly in the style sheet:
<div class=example>
<pre highlight="css">body { column-count: 2 }</pre>
In this case, the number of columns is fixed
and the column widths will vary depending on the available width.
</div>
The shorthand 'columns' property can be used to set either,
or both, properties in one declaration.
<div class=example>
In these examples, the number of columns, the width of columns,
10BC8
and
both the number and width are set, respectively:
<pre highlight="css">
body { columns: 2 }
body { columns: 12em }
body { columns: 2 12em }
</pre>
</div>
Another group of properties introduced in this module describe
gaps and rules between columns.
<div class=example>
<pre highlight="css">
body {
column-gap: 1em;
column-rule: thin solid black;
}
</pre>
The first declaration in the example above sets the gap
between two adjacent columns to be 1em.
Column gaps are similar to padding areas.
In the middle of the gap there will be a rule
which is described by the 'column-rule' property.
</div>
The values of the 'column-rule' property are similar to those of the CSS 'border' properties.
Like 'border', 'column-rule' is a shorthand property.
<div class=example>
In this example, the shorthand 'column-rule' declaration from the
above example has been expanded:
<pre highlight="css">
body {
column-gap: 1em;
column-rule-width: thin;
column-rule-style: solid;
column-rule-color: black;
}
</pre>
</div>
The 'column-fill' and 'column-span' properties
give style sheets a wider range of visual expressions in multi-column layouts.
<div class=example>
In this example, columns are set to be balanced,
i.e., to have approximately the same length.
Also, <code>h2</code> elements are set to span across all columns.
<pre highlight="css">
div { column-fill: balance }
h2 { column-span: all }
</pre>
</div>
This specification introduces ten new properties,
all of which are used in the examples above.
If all column properties have their initial value,
the layout of an element will be identical
to a multi-column layout with only one column.
<div class="example">
<a>Column gaps</a> (diagonal hatching) and <a>column rules</a>
are shown in this sample rendition of a multi-column container
with padding (cross hatching).
The hatched areas are present for illustrational purposes only.
In actual implementations these areas will be determined by the background,
the second image shows a rendering of a [=multi-column container=] with column-rules.
<figure>
<img alt="a diagram showing the various parts of multi-column layout" src="images/initial-example.svg" no-autosize>
<img alt="key to the conventions used to display invisible parts of diagram" src="images/invisible-elements.svg" no-autosize>
<figcaption>A multi-column layout with the non-visible column-span and padding inside the multicol container highlighted.</figcaption>
</figure>
<figure>
<img alt="a diagram showing the various parts of multi-column layout" src="images/initial-example-b.svg" no-autosize>
<figcaption>The same layout as in the first image, as it would be displayed by an implementation.</figcaption>
</figure>
</div>
<h3 id="values">
Value Definitions</h3>
This specification follows the <a href="https://www.w3.org/TR/CSS2/about.html#property-defs">CSS property definition conventions</a> from [[!CSS21]]
using the <a href="https://www.w3.org/TR/css-values-3/#value-defs">value definition syntax</a> from [[!CSS-VALUES-3]].
Value types not defined in this specification are defined in CSS Values & Units [[!CSS-VALUES-3]].
Combination with other CSS modules may expand the definitions of these value types.
In addition to the property-specific values listed in their definitions,
all properties defined in this specification
also accept the <a>CSS-wide keywords</a> as their property value.
For readability they have not been repeated explicitly.
<h2 id="the-multi-column-model">
The Multi-Column Model</h2>
An element whose 'column-width' or 'column-count' property is not ''column-width/auto''
establishes a <dfn lt="multi-column container|multicol container" oldids="multi-column-element" export>multi-column container</dfn>
(or <i>multicol container</i> for short),
and therefore acts as a container for [=multi-column layout=].
<wpt title="Basic multicol tests.">
multicol-basic-002.html
multicol-basic-004.html
</wpt>
<wpt title="Tests demonstrating that auto values do not create a multicol container.">
multicol-count-computed-004.xht
</wpt>
<wpt title="Multicol properties do not inherit.">
inheritance.html
</wpt>
<wpt title="Multicol with scrolled columns.">
multicol-scroll-content.html
</wpt>
<wpt title="Multicol with zero height.">
multicol-zero-height-001.xht
multicol-zero-height-002.html
multicol-zero-height-003.html
</wpt>
In the traditional CSS box model,
the content of an element is
flowed into the content box of the corresponding element.
Multi-column layout introduces a [=fragmentation context=]
formed of <a lt="anonymous box">anonymous</a> [=fragmentation containers=]
called <dfn export lt="column box" local-lt=column>column boxes</dfn>
(or <i>columns</i> for short).
These [=column boxes=] establish
an independent [=block formatting context=]
into which the multi-column container's content flows,
and form the [=containing block=] for its non-positioned children.
<div class=example>
In this example, the width of the image is set with these rules:
<pre highlight="css">
img {
display: block;
width: 100%;
}
</pre>
Given that the column box creates a new [=block formatting context=],
the 'width' is calculated relative to the column box.
Therefore the image will not overflow the column box:
<figure>
<img src="images/image-inside-column.svg" alt="an image contained inside a column box" no-autosize>
<figcaption>The image is constrained by the column box that it is displayed in.</figcaption>
</figure>
</div>
<div class="example">
Given that the column box creates a new [=block formatting context=], a top margin set on the first child element of a multicol container will not collapse with the margins of the multicol container.
<figure>
<img src="images/margins-do-not-collapse.svg" alt="The first paragraph has a 'margin-top' of ''1em'', which appears before the text." no-autosize>
<figcaption>The margin above the first paragraph has not collapsed, leaving a ''1em'' margin above the first line in the multicol container.</figcaption>
</figure>
</div>
<wpt>
multicol-margin-001.xht
multicol-margin-002.xht
multicol-margin-003.html
multicol-margin-child-001.xht
multicol-nested-margin-001.xht
multicol-nested-margin-002.xht
multicol-nested-margin-003.xht
multicol-nested-margin-004.xht
multicol-nested-margin-005.xht
multicol-collapsing-001.xht
</wpt>
Floats that appear inside multi-column layouts are positioned with
regard to the [=column box=] where the float appears.
<div class="example">
In this example, this CSS fragment describes the presentation of the image:
<pre highlight="css">
img {
display: block;
float: right;
}
</pre>
In the HTML, the image appears after the sentence ending, "the leg of a chicken".
<figure>
<img src="images/image-floated-in-column.svg" alt="an image floated and contained inside a column box" no-autosize>
<figcaption>The image is floated inside the column box it appears in.</figcaption>
</figure>
</div>
Content overflowing a [=column box=] in the [=block axis=]
[=fragments=] and continues in the next [=column box=].
Note: Column boxes, which are [=anonymous boxes=],
do not become the [=containing block=]
for [=absolutely positioned boxes=].
The 'position' property, which establishes a containing block for such boxes,
applies to the [=multicol container=], it being the [=principal box=].
<wpt>
multicol-containing-001.xht
multicol-containing-002.xht
multicol-containing-003.xht
multicol-containing-003.html
multicol-contained-absolute.html
abspos-autopos-contained-by-viewport-000.html
abspos-autopos-contained-by-viewport-001.html
abspos-multicol-in-second-outer-clipped.html
</wpt>
<div class="example">
In this example, the [=multi-column container=] has ''position: relative''
thus becoming the containing block.
The image is a direct child of the [=multi-column container=]
and has ''position: absolute''.
It takes positioning from the [=multi-column container=]
and not from the [=column box=].
<pre highlight="css">
.container {
position: relative;
column-count: 3;
}
img {
position: absolute;
top: 20px;
left: 40px;
}
</pre>
<figure>
<img src="images/column-not-containing-block.svg" alt="The absolutely positioned image is positioned by reference to the [=multi-column container=] not the [=column box=]." no-autosize>
<figcaption>The figure demonstrates that the absolutely positioned image is positioned by reference to the multicol container and not the column box.</figcaption>
</figure>
</div>
Out-of-flow descendants of a [=multi-column container=] do affect column balancing,
and the block-size of the [=multi-column container=].
<wpt>
multicol-oof-inline-cb-001.html
multicol-oof-inline-cb-002.html
</wpt>
The column boxes are ordered
in the [=inline base direction=] of the multicol container
and arranged into
10BC8
<dfn lt="multi-column line | multi-col line | multicol line">multicol lines</dfn>.
The <dfn export>column width</dfn> is the length of the column box in the inline direction.
The <dfn export>column height</dfn> is the length of the column box in the block direction.
All column boxes in a line have the same column width,
and all column boxes in a line have the same column height.
<wpt title="The following tests relate to baseline alignment of the content of columns,
though this is not defined in this specification.">
baseline-000.html
baseline-001.html
baseline-002.html
baseline-003.html
baseline-004.html
baseline-005.html
baseline-006.html
baseline-007.html
baseline-008.html
crashtests/as-baseline-aligned-grid-item.html
</wpt>
<wpt title="The following tests check the behavior of list items that are also muticol containers.">
multicol-list-item-001.xht
multicol-list-item-002.html
multicol-list-item-003.html
multicol-list-item-004.html
multicol-list-item-005.html
multicol-list-item-006.html
multicol-list-item-007.html
multicol-list-item-008.html
</wpt>
<wpt title="Testing grid items inside multicol">
balance-grid-001.html
</wpt>
<wpt title="The following tests check the behavior of table elements.">
table/multicol-table-cell-001.xht
table/multicol-table-cell-height-001.xht
table/multicol-table-cell-height-002.xht
table/multicol-table-cell-vertical-align-001.xht
table/table-cell-as-multicol.html
table/table-cell-content-change-000.html
table/table-cell-content-change-001.html
table/table-cell-multicol-nested-001.html
table/table-cell-multicol-nested-002.html
table/table-cell-multicol-nested-003.html
crashtests/break-before-multicol-caption.html
crashtests/table-cell-writing-mode-root.html
table/balance-breakafter-before-table-section-crash.html
table/balance-table-with-border-spacing.html
table/balance-table-with-fractional-height-row.html
</wpt>
<wpt title="The following tests check that paint order is correct.">
float-and-block.html
move-with-text-after-paint.html
resize-with-text-after-paint.html
</wpt>
<wpt title="The following tests relate to animation or transformation of multicol properties.">
animation/column-width-interpolation.html
animation/discrete-no-interpolation.html
multicol-overflow-positioned-transform-001.html
multicol-overflow-transform-001.html
resize-multicol-with-fixed-size-children.html
resize-in-strict-containment-nested.html
remove-child-in-strict-containment-also-spanner.html
composited-under-clip-under-multicol.html
change-intrinsic-width.html
change-fragmentainer-size-000.html
change-fragmentainer-size-001.html
change-fragmentainer-size-002.html
change-fragmentainer-size-003.html
hit-test-child-under-perspective.html
hit-test-transformed-child.html
</wpt>
<wpt title="Tests related to implementation bugs, not linked to specific normative text.">
crashtests/multicol-with-monolithic-oof-with-multicol-with-oof.html
crashtests/chrome-bug-1293905.html
crashtests/chrome-bug-1297118.html
crashtests/chrome-bug-1301281.html
crashtests/chrome-bug-1303256.html
crashtests/chrome-bug-1314866.html
crashtests/dynamic-simplified-layout-break-propagation.html
crashtests/float-multicol-crash.html
change-abspos-width-in-second-column-crash.html
change-out-of-flow-type-and-remove-inner-multicol-crash.html
crashtests/monolithic-oof-in-clipped-container.html
crashtests/move-linebreak-to-different-column.html
crashtests/move-newline-pre-text.html
crashtests/multicol-at-page-boundary-print.html
crashtests/multicol-block-in-inline-crash.html
crashtests/multicol-cached-consumed-bsize-crash.html
crashtests/multicol-column-change-crash.html
crashtests/multicol-dynamic-contain-crash.html
crashtests/multicol-dynamic-transform-crash.html
crashtests/multicol-floats-in-ifc.html
crashtests/multicol-parallel-flow-after-spanner-in-inline.html
crashtests/outline-move-oof-with-inline.html
crashtests/relpos-inline-with-abspos-multicol-gets-block-child.html
crashtests/size-containment-become-multicol-add-inline-child.html
crashtests/sticky-in-abs-in-sticky.html
crashtests/vertical-rl-column-rules-wide-columns.html
dynamic-become-multicol-add-oof-inside-inline-crash.html
extremely-tall-multicol-with-extremely-tall-child-crash.html
file-control-crash.html
img-alt-as-multicol-crash.html
overflow-scroll-in-multicol-crash.html
remove-block-sibling-of-inline-with-block-crash.html
subpixel-scroll-crash.html
text-child-crash.html
with-custom-layout-on-same-element-crash.https.html
crashtests/oof-in-area-001.html
crashtests/oof-in-area-002.html
crashtests/oof-in-area-003.html
crashtests/oof-in-oof-multicol-in-multicol-spanner-in-multicol.html
crashtests/oof-in-oof-multicol-in-relpos-in-oof-in-multicol-in-multicol.html
crashtests/oof-in-oof-multicol-in-relpos-spanner-in-multicol-in-relpos-multicol-in-multicol.html
crashtests/oof-in-oof-multicol-in-relpos-spanner-in-spanner-multicol-in-multicol-in-multicol.html
crashtests/oof-in-oof-multicol-in-spanner-in-multicol-in-spanner-in-nested-multicol.html
crashtests/oof-in-oof-multicol-in-spanner-in-nested-multicol.html
crashtests/oof-in-relpos-in-oof-multicol-in-oof-in-relpos-in-oof-multicol-in-multicol.html
crashtests/oof-in-relpos-in-oof-multicol-in-relpos-in-oof-multicol-in-relpos-multicol.html
crashtests/floated-input-in-inline-next-column.html
crashtests/inline-float-parallel-flow.html
crashtests/table-caption-in-clipped-overflow.html
crashtests/text-in-inline-interrupted-by-float.html
increase-prev-sibling-height.html
crashtests/interleaved-bfc-crash.html
crashtests/relayout-fixedpos-in-abspos-in-relpos-in-nested-multicol.html
crashtests/inline-become-oof-container-make-oof-inflow.html
multicol-dynamic-change-inside-break-inside-avoid-001.html
multicol-dynamic-add-001.html
scroll-width-height.tentative.html
filter-with-abspos.html
crashtests/add-list-item-marker.html
</wpt>
<wpt title="Tests related to printing and paged media as related to multicol.">
auto-fill-auto-size-001-print.html
auto-fill-auto-size-002-print.html
multicol-height-002-print.xht
named-page.html
page-property-ignored.html
</wpt>
Note: In text set using a vertical writing mode,
the block direction runs horizontally.
In a vertical writing mode columns are laid out horizontally,
and the direction of the flow of blocks may be right to left, or left to right.
The 'column-width' property therefore refers to the inline size of the column,
and not the physical horizontal width.
<div class="example">
<figure>
<img alt="The first image shows horizontal text with a LTR inline direction. The second shows vertical text with blocks flowing right to left. The third shows vertical text with blocks flowing left to right." src="images/writing-modes.svg" no-autosize>
<figcaption>A diagram showing the different ways columns may be arranged due to writing mode.
<br>From left to right: horizontal-tb, vertical-rl, vertical-lr.</figcaption>
</figure>
</div>
<wpt title="Tests regarding vertical writing modes.">
orthogonal-writing-mode-shrink-to-fit.html
multicol-under-vertical-rl-scroll.html
hit-test-in-vertical-rl.html
</wpt>
Within each [=multicol line=] in the multi-column container,
adjacent column boxes are separated by a <dfn noexport>column gap</dfn>,
which may contain a <dfn noexport>column rule</dfn>.
All column gaps in the same multi-column container are equal.
All column rules in the same multi-column container are also equal, if they appear;
column rules only appear between columns that both have content.
In the simplest case a multicol container will contain only one line
of columns, and the height of each column will be equivalent to the
used height of the multi-column container's content box.
However, [=fragmentation=] or [=spanners=]
can split the content of the [=multi-column container=]
into multiple [=multicol lines=].
If the multi-column container is paginated, the height of each column is
constrained by the page and the content continues in a new line of
column boxes on the next page; a column box never splits across pages.
The same effect occurs when a <i>spanning element</i> divides the
multi-column container: the columns before the spanning element are
balanced and shortened to fit their content. Content after the
spanning element then flows into a new, subsequent line of column boxes.
<div class="example">
<figure>
<img alt="a diagram showing a spanning element causing the shortened columns above the element with text continuing in new columns below" src="images/simple-span-example.svg" no-autosize>
<figcaption>A demonstration of how the spanning element divides the multicol container.</figcaption>
</figure>
</div>
A [=multi-column container=] therefore is a regular [=block container=]
that establishes a new [=independent formatting context=]
whose contents consist of a series of
[=multicol lines=] and multicol spanners.
Each [=multi-column line=] acts as a [=block-level box=]
that establishes a <dfn>multi-column formatting context</dfn>
for its [=column boxes=];
and each [=spanner=] acts as a [=block-level box=]
that establishes an [=independent formatting context=]
with its type depending on its 'display' value as usual.
Nested multi-column containers are allowed,
but there may be implementation-specific limits.
<wpt>
multicol-nested-002.xht
multicol-nested-005.xht
multicol-nested-006.html
multicol-nested-007.html
multicol-nested-008.html
multicol-nested-009.html
multicol-nested-010.html
multicol-nested-011.html
multicol-nested-012.html
multicol-nested-013.html
multicol-nested-014.html
multicol-nested-015.html
multicol-nested-016.html
multicol-nested-017.html
multicol-nested-018.html
multicol-nested-019.html
multicol-nested-020.html
multicol-nested-021.html
multicol-nested-022.html
multicol-nested-023.html
multicol-nested-024.html
multicol-nested-025.html
multicol-nested-026.html
multicol-nested-027.html
multicol-nested-028.html
multicol-nested-029.html
multicol-nested-030.html
multicol-nested-031.html
crashtests/nested-as-balanced-legend.html
crashtests/nested-as-nested-balanced-legend.html
crashtests/nested-floated-multicol-with-tall-margin.html
crashtests/nested-multicol-and-float-with-tall-padding-before-float.html
crashtests/nested-multicol-and-float-with-tall-padding.html
crashtests/nested-multicol-fieldset-tall-trailing-border-freeze.html
crashtests/nested-multicol-fieldset-tall-trailing-padding.html
crashtests/nested-multicol-in-svg-foreignobject.html
crashtests/nested-multicol-nested-flex.html
crashtests/nested-multicol-with-float-between.html
crashtests/nested-oof-multicol-with-monolithic-child.html
crashtests/nested-oof-multicol-with-oof-needing-additional-columns.html
crashtests/nested-oof-multicol-with-padding.html
crashtests/nested-with-fragmented-oof-negative-top-offset.html
crashtests/nested-with-multicol-table-caption.html
crashtests/multicol-table-caption-parallel-flow-after-spanner-in-inline.html
crashtests/nested-with-multicol-table-cell.html
crashtests/nested-with-oof-inside-fixed-width.html
crashtests/nested-with-percentage-size-and-oof.html
crashtests/nested-with-tall-padding-and-oof.html
crashtests/nested-with-tall-padding.html
crashtests/oof-in-nested-line-float.html
crashtests/oof-nested-multicol-inside-oof.html
crashtests/relayout-nested-with-oof.html
crashtests/repeated-section-in-nested-table-nested-multicol.html
crashtests/repeated-table-footer-in-caption-nested-multicol.html
nested-balanced-monolithic-multicol-crash.html
nested-balanced-very-tall-content-crash.html
nested-floated-shape-outside-multicol-with-monolithic-child-crash.html
nested-with-overflowing-padding-crash.html
triply-nested-with-fixedpos-in-abspos-crash.html
fixed-in-nested-multicol-with-transform-container.html
fixed-in-nested-multicol-with-viewport-container.html
fixed-in-nested-multicol.html
nested-after-float-clearance.html
nested-at-outer-boundary-as-fieldset.html
nested-at-outer-boundary-as-float.html
nested-at-outer-boundary-as-legend.html
nested-floated-multicol-with-monolithic-child.html
nested-oofs-in-relative-multicol.html
nested-past-fragmentation-line.html
nested-with-too-tall-line.html
oof-nested-in-single-column.html
nested-non-auto-inline-size-offset-top.html
fixedpos-static-pos-with-viewport-cb-001.html
fixedpos-static-pos-with-viewport-cb-002.html
fixedpos-static-pos-with-viewport-cb-003.html
multicol-height-block-child-001.xht
</wpt>
Note: It is not possible to set properties/values on column boxes.
For example, the background of a certain column box cannot be set
and a column box has no concept of padding, margin or borders.
Future specifications may add additional functionality.
For example, columns of different widths and different backgrounds may be supported.
Note: Multicol containers with column heights larger than the viewport may pose accessibility issues.
See <a href="#a11y">Accessibility Considerations</a> for more details.
<h2 id="the-number-and-width-of-columns">
The Number and Width of Columns</h2>
Finding the number and width of columns is fundamental when laying out multi-column content.
These properties are used to set the number and width of columns:
<ul>
<li>'column-count'</li>
<li>'column-width'</li>
</ul>
A third property, 'columns',
is a shorthand property which sets both 'column-width' and 'column-count'.
Other factors, such as explicit column breaks, content, and height constraints,
may influence the actual number and width of columns.
<h3 id='cw'>The Inline Size of Columns: the 'column-width' property</h3>
<pre class=propdef>
Name: column-width
Value: auto | <<length [0,∞]>>
Initial: auto
Applies to: <a>block containers</a> except <a>table wrapper boxes</a>
Inherited: no
Percentages: N/A
Computed value: the keyword ''auto'' or an absolute length
Animation type: by computed value type
</pre>
This property describes the width of columns in multicol containers.
<dl dfn-type=value dfn-for=column-width>
<dt><dfn>auto</dfn></dt>
<dd>
means that the column width will be determined by other properties
(e.g., 'column-count', if it has a non-auto value).
<dt><dfn><<length [0,∞]>></dfn>
<dd>
describes the optimal column width.
The actual column width may be wider (to fill the available space),
or narrower (only if the available space is smaller than the specified column width).
Negative values are not allowed.
Used values will be clamped to a minimum of ''1px''.
<wpt>
zero-column-width-computed-style.html
zero-column-width-layout.html
</wpt>
</dd>
</dl>
<wpt>
multicol-basic-003.html
multicol-basic-008.xht
multicol-reduce-000.xht
multicol-width-001.xht
multicol-width-002.xht
multicol-width-003.xht
multicol-width-005.html
multicol-width-ch-001.xht
multicol-width-negative-001.xht
multicol-width-invalid-001.xht
multicol-width-large-001.xht
multicol-width-large-002.xht
multicol-inherit-003.xht
parsing/column-width-computed.html
parsing/column-width-invalid.html
parsing/column-width-valid.html
multicol-width-small-001.xht
</wpt>
<div class="example">
For example, consider this style sheet:
<pre highlight="css">
div {
width: 100px;
column-width: 45px;
column-gap: 0;
column-rule: none;
}
</pre>
There is room for two ''45px'' wide columns inside the ''100px'' wide element.
In order to fill the available space
the actual column width will be increased to ''50px''.
</div>
<div class="example">
Also, consider this style sheet:
<pre highlight="css">
div {
width: 40px;
column-width: 45px;
column-gap: 0;
column-rule: none;
}
</pre>
The available space is smaller than the specified column width
and the actual column width will therefore be decreased.
</div>
To ensure that 'column-width' can be used with vertical text,
column width means the length of the line boxes inside the columns.
Note: The reason for making 'column-width' somewhat flexible
is to achieve scalable designs that can fit many screen sizes.
To set an exact column width,
the column gap and the width of the multicol container (assuming horizontal text)
must also be specified.
<h3 id='cc'>The Number of Columns: the 'column-count' property</h3>
<pre class=propdef>
Name: column-count
Value: auto | <<integer [1,∞]>>
Initial: auto
Applies to: <a>block containers</a> except <a>table wrapper boxes</a>
Inherited: no
Percentages: N/A
Computed value: specified value
Animation Type: by computed value
</pre>
This property describes the number of columns of a [=multicol container=].
<dl dfn-type=value dfn-for=column-count>
<dt><dfn>auto</dfn>
<dd>
means that the number of columns will be determined by other properties
(e.g., 'column-width', if it has a non-auto value).
<dt><dfn><<integer [1,∞]>></dfn>
<dd>
describes the optimal number of columns into which the content of the element will be flowed.
Values must be greater than 0.
If both 'column-width' and 'column-count' have non-auto values,
the integer value describes the maximum number of columns.
</dd>
</dl>
<wpt>
multicol-count-001.xht
multicol-count-002.xht
multicol-basic-006.xht
multicol-width-count-001.xht
multicol-width-count-002.xht
multicol-columns-toolong-001.xht
multicol-count-negative-001.xht
multicol-count-negative-002.xht
multicol-count-non-integer-001.xht
multicol-count-non-integer-002.xht
multicol-count-non-integer-003.xht
multicol-inherit-001.xht
multicol-inherit-002.xht
parsing/column-count-invalid.html
parsing/column-count-valid.html
parsing/column-count-computed.html
animation/column-count-interpolation.html
large-actual-column-count.html
with-custom-layout-on-same-element.https.html
</wpt>
<div class="example">
Example:
<pre highlight="css">body { column-count: 3 }</pre>
</div>
<h3 id="columns">The 'column-width' and 'column-count' Shorthand: The 'columns' Property</h3>
<pre class="propdef shorthand">
Name: columns
Value: <<'column-width'>> || <<'column-count'>>
</pre>
This is a shorthand property for setting 'column-width' and 'column-count'.
Omitted values are set to their initial values.
<div class="example">
Here are some valid declarations using the 'columns' property:
<pre highlight="css">
columns: 12em; /* column-width: 12em; column-count: auto */
columns: auto 12em; /* column-width: 12em; column-count: auto */
columns: 2; /* column-width: auto; column-count: 2 */
columns: 2 auto; /* column-width: auto; column-count: 2 */
columns: auto; /* column-width: auto; column-count: auto */
columns: auto auto; /* column-width: auto; column-count: auto */
</pre>
</div>
<wpt>
multicol-columns-001.xht
multicol-columns-002.xht
multicol-columns-003.xht
multicol-columns-004.xht
multicol-columns-005.xht
multicol-columns-006.xht
multicol-columns-007.xht
multicol-columns-invalid-001.xht
multicol-columns-invalid-002.xht
multicol-basic-001.html
multicol-basic-003.html
multicol-basic-005.xht
multicol-basic-007.xht
parsing/columns-invalid.html
parsing/columns-valid.html
</wpt>
<h3 id="pseudo-algorithm">The Pseudo-algorithm</h3>
The pseudo-algorithm below determines the used values for
'
9C9A
;column-count' (N) and 'column-width' (W). There is one other variable
in the pseudo-algorithm: U is the used width of the multi-column container.
Note: The used width U of the multi-column container can depend on the element's contents,
in which case it also depends on the computed values of the 'column-count' and 'column-width' properties.
This specification does not define how U is calculated.
Another module (probably the Basic Box Model [[CSS3BOX]]
or the Box Sizing Module [[CSS3-SIZING]]) is expected to define this.
<wpt>
intrinsic-size-001.html
intrinsic-size-002.html
intrinsic-size-003.html
intrinsic-size-004.html
intrinsic-size-005.html
as-column-flex-item.html
intrinsic-width-change-column-count.html
</wpt>
<!--
Two assumptions are being made by the pseudo-algorithm:
<ul>
<li>that the block direction is unconstrained
<li>that no column breaks are added through style sheets
</ul>
-->
The <code>floor(X)</code> function returns the largest integer Y ≤ X.
<pre>
(01) if ((column-width = auto) and (column-count = auto)) then
(02) exit; /* not a multicol container */
(03) if column-width = auto then
(04) N := column-count
(05) else if column-count = auto then
(06) N := max(1,
(07) floor((U + column-gap)/(column-width + column-gap)))
(08) else
(09) N := min(column-count, max(1,
(10) floor((U + column-gap)/(column-width + column-gap))))
</pre>
And:
<pre>
(11) W := max(0, ((U + column-gap)/N - column-gap))
</pre>
For the purpose of finding the number of auto-repeated columns,
the UA must floor the column size to a UA-specified value to avoid division by zero.
It is suggested that this floor be 1px or less.
In fragmented contexts such as in [=paged media=],
user agents may perform this calculation on a per-fragment basis.
The used value for 'column-count' is calculated without regard for explicit column breaks or constrained column heights,
while the actual value takes these into consideration.
<wpt>
column-count-used-001.html
</wpt>
<div class="example">
In this example, the actual column-count is higher than the used column-count
due to explicit column breaks:
<pre highlight="css">
div {
width: 40em;
columns: 20em;
column-gap: 0;
}
p {
break-after: column;
}
</pre>
<pre highlight="html">
<div>
<p>one
<p>two
<p>three
</div>
</pre>
<figure>
<img src="images/column-count-higher-than-used-count.svg" alt="Two columns drawn inside the container, one outside" no-autosize>
<figcaption>The computed column-count is auto, the used column-count is 2 and the actual column-count is 3.</figcaption>
</figure>
</div>
<div class=example>
The actual column-count may be lower than the used column-count.
Consider this example:
<pre highlight="css">
div {
width: 80em;
height: 10em;
columns: 20em;
column-gap: 0;
column-fill: auto;
}
</pre>
<pre highlight="html">
<div>foo</div>
</pre>
The computed column-count is auto,
the used column-count is 4,
and the actual column-count is 1.