While Bootstrap uses ems or rems for defining most sizes, pxs are used for grid breakpoints and container widths. This is because the viewport width is in pixels and does not change with the font size. See how aspects of the Bootstrap grid system work across multiple devices with a handy table.
Extra small
<576px
Small
≥576px
Medium
≥768px
Large
≥992px
Extra large
≥1200px
Max container width
None (auto)
540px
720px
960px
1140px
Class prefix
.col-
.col-sm-
.col-md-
.col-lg-
.col-xl-
# of columns
12
Gutter width
30px (15px on each side of a column)
Nestable
Yes
Column ordering
Yes
Grid Example
Using a single set of .col-md-* grid classes, you can create a basic grid system that starts out stacked on mobile devices and tablet devices (the extra small to small range) before becoming horizontal on desktop (medium) devices. Place grid columns within any .row.
.col-sm-1
.col-sm-1
.col-sm-1
.col-sm-1
.col-sm-1
.col-sm-1
.col-sm-1
.col-sm-1
.col-sm-1
.col-sm-1
.col-sm-1
.col-sm-1
.col-sm-2
.col-sm-2
.col-sm-2
.col-sm-2
.col-sm-2
.col-sm-2
.col-sm-3
.col-sm-3
.col-sm-3
.col-sm-3
.col-sm-4
.col-sm-4
.col-sm-4
.col-sm-6
.col-sm-6
.col-sm-12
Variable width content
Use col-{breakpoint}-auto classes to size columns based on the natural width of their content.
1 of 3
Variable width content
3 of 3
1 of 3
Variable width content
3 of 3
Reordering
Use .order- classes for controlling the visual order of your content. These classes are responsive, so you can set the order by breakpoint (e.g., .order-1.order-md-2). Includes support for 1 through 12 across all five grid tiers.
First, but unordered
Second, but last
Third, but first
There are also responsive .order-first and .order-last classes that change the order of an element by applying order: -1 and order: 13 (order: $columns + 1), respectively. These classes can also be intermixed with the numbered .order-* classes as needed.
First, but last
Second, but unordered
Third, but first
Offsetting columns
Move columns to the right using .offset-md-* classes. These classes increase the left margin of a column by * columns. For example, .offset-md-4 moves .col-md-4 over four columns.
.col-md-4
.col-md-4 .offset-md-4
.col-md-3 .offset-md-3
.col-md-3 .offset-md-3
.col-md-6 .offset-md-3
Nesting
To nest your content with the default grid, add a new .row and set of .col-sm-* columns within an existing .col-sm-* column. Nested rows should include a set of columns that add up to 12 or fewer (it is not required that you use all 12 available columns).
Level 1: .col-sm-9
Level 2: .col-8 .col-sm-6
Level 2: .col-4 .col-sm-6
Horizontal alignment
Use flexbox alignment utilities to vertically and horizontally align columns.
One of two columns
One of two columns
One of two columns
One of two columns
One of two columns
One of two columns
One of two columns
One of two columns
One of two columns
One of two columns
Vertical alignment
Use flexbox alignment utilities to vertically and horizontally align columns.
