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CSS box-sizing Property

The box-sizing property defines how the browser should calculate the total width and height of an element: should they include padding and borders, or not.

CSS Demo: box-sizing

width: 250px;
height: 150px;
padding: 40px;
border: 3px solid #ccc;
box-sizing: content-box;
width: 250px;
height: 150px;
padding: 40px;
border: 3px solid #ccc;
box-sizing: border-box;
This div's width is 250px and height is 150px

By default in the CSS box model, the width and height you assign to an element is applied only to the element's content box. If the element has any border or padding, the size of the element will be increased. This means that when you set width and height, you have to adjust the value you give to allow for any border or padding that may be added.

If you set box-sizing: border-box; on an element, padding and border are included in the width and height.

Technical Details

Default value content-box
Applies to all elements
Inherited no
Computed value as specified
Animatable no See animatable properties.
Version CSS3
JavaScript syntax object.style.boxSizing = "border-box" Demo


CSS Syntax:

box-sizing: content-box|border-box|initial|inherit;

Examples

The following example shows how to use box-sizing property:

Run code

Browser compatibility

The numbers in the table specify the first browser version that fully supports the box-sizing property.

Numbers followed by -webkit- and -moz- specify the first version that worked with a vendor prefix.

Property
box-sizing 10
4 -webkit-
29
2 -moz-
9.5 5.1
3.2 -webkit-
8

Property Values

The following table describes the values of box-sizing property:

Value Description
border-box The specified width and height properties include the padding and border, but not the margin.
content-box The specified width and height properties include only the content of the element. It does not include the padding, border or margin (This is default)
initial Sets this property to its default value
inherit Inherits this property from its parent element

See also

CSS box sizing tutorial