Basic Concepts of Multicol

Multiple-column Layout, usually referred to as multicol, is a specification for laying out content into a set of column boxes much like columns in a newspaper. This guide explains how the specification works with some common use case examples.

Key Concepts and Terminology

Multicol is unlike any of the other layout methods we have in CSS in that it fragments the content, including all descendent elements, into columns. This happens in the same way that content is fragmented into pages when we work with CSS Paged Media, for example by creating a print stylesheet.

The properties defined by the specification are:

• column-width
• column-count
• columns
• column-rule-color
• column-rule-style
• column-rule-width
• column-rule
• column-span
• column-fill
• column-gap

By adding column-count or column-width to an element, that element becomes a multi-column container, or multicol container for short. The columns are anonymous boxes and described as column boxes in the specification.

Defining columns

To create a multicol container you must use at least one of the column-* properties, these being column-count and column-width.

The column-count property

The column-count property specifies the number of columns that you would like the content to be displayed as. The browser will then assign the correct amount of space to each column box to create the requested number of columns.

In the below example we use the column-count property to create three columns on the .container element. The content, including the children of .container is then split between the three columns.

In the above example the content is wrapped in paragraph p tags with default styling. Therefore, there is a margin above each paragraph. You can see how this margin causes the first line of text to be pushed down. This is because a multicol container creates a new Block Formatting Context (BFC) which means margins on child elements do not collapse with any margin on the container.

The column-width property

The column-width property is used to set the optimal width for every column box. If you declare a column-width, the browser will work out how many columns of that width will fit into the multicol container and distribute any extra space equally between the columns. Therefore, the column width should be seen as a minimum width, as column boxes are likely to be wider due to the additional space.

The column box will only shrink to be smaller than the declared column width in the case of a single column with less available width than the value of column-width.

In the below example we use the column-width property with a value of 200px. We get as many 200 pixel columns as will fit the container, with the extra space shared equally.

Using column-count and column-width together

If you specify both properties on a multicol container then column-count will act as a maximum number of columns. Therefore the behavior as described for column-width will happen, until the number of columns in column-count is reached. After this point no more columns will be drawn, and the extra space is distributed evenly between the existing columns, even if there is enough room for more columns of the specified column-width size.

When using both properties together you may get fewer columns than specified in the value for column-count.

In this next example we use column-width of 200px and column-count of 2. Even if there is space for more than two columns, we get two. If there is not enough space for two columns of 200px, however, we get one.

The columns shorthand

You can use the columnsshorthand to set column-count and column-width. If you set a length unit, this will be used for column-width, set an integer and it will be used for column-count. You can set both, separating the two values with a space.

This CSS would give the same result as example 1, column-count set to 3.

.container {
  columns: 3;
}

This CSS would give the same result as example 2, with column-width of 200px.

.container {
  columns: 200px;
}

This CSS would give the same result as example 3, with both column-count and column-width set.

.container {
  columns: 2 200px;
}

Next Steps

In this guide we've learned the basic use of Multiple-column Layout. In the next guide, we will look at how much we can style the columns themselves.