CSS box-sizing Property

Description

The box-sizing property is used to alter the default CSS box model used to calculate widths and heights of elements.
According to the CSS specification, the width of the block is the sum of the width of the content, margin, padding, and border values. The situation is similar with the block height. The box-sizing property allows you to change this algorithm so that the width and height properties do not specify the dimensions of the content, but the dimensions of the block.

Initial value: content-box
Applies to: All elements that accept width or height
Inherited: No
Computed value: Specified value
Animatable: No
JavaScript syntax: object.style.boxSizing

Interactive Demo

box-sizing: content-box;
width: 100%;

box-sizing: content-box;
width: 100%;
border: solid #5B6DCD 10px;
padding: 5px;

box-sizing: border-box;
width: 100%;
border: solid #5B6DCD 10px;
padding: 5px;

Parent container

Child container

Syntax

box-sizing: content-box | padding-box | border-box | inherit

Values

content-boxThis is the default style as specified by the CSS standard. The width and height properties are measured including only the content, but not the border, margin, or padding.
padding-boxThe width and height properties include the padding size, and do not include the border or margin.
border-boxThe width and height properties include the padding and border, but not the margin. This is the box model used by Internet Explorer when the document is in Quirks mode

Example

HTML

<div class="test">content-box</div> 

<div class="test2">border-box</div>

CSS

div { 
   display: inline-block;  
   width: 150px; 
   height: 150px;  
   margin: 10px;  
   padding: 10px; 
   border: 10px solid green;  
} 
.test { 
   box-sizing: content-box;  
} 
.test2 { 
   box-sizing: border-box;  
}

Result

Editor