This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for the proper prefixes to use in various browsers. Also note that the syntax and behavior of an experimental technology is subject to change in future versions of browsers as the spec changes.
Summary
The box-sizing property is used to alter the default CSS box model used to calculate width and height of the elements. It is possible to use this property to emulate the behavior of browsers that do not correctly support the CSS box model specification.
| Initial value | content-box |
|---|---|
| Applies to | all elements that accept width or height |
| Inherited | no |
| Media | visual |
| Computed value | as specified |
| Animatable | no |
| Canonical order | the unique non-ambiguous order defined by the formal grammar |
Syntax
/* Keyword values */ box-sizing: content-box; box-sizing: border-box; /* Global values */ box-sizing: inherit; box-sizing: initial; box-sizing: unset;
Values
content-box- This is the initial and default value as specified by the CSS standard. The
widthandheightproperties are measured including only the content, but not the padding, border or margin. Note: Padding, border & margin will be outside of the box e.g. IF .box {width: 350px}; THEN you apply {border: 10px solid black;} RESULT {rendered in the browser} .box {width: 370px;} - So simply the dimension of element is calculated as, width = width of the content, and height = height of the content (excluding the values of border and padding).
border-box- The
widthandheightproperties 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. Note that padding and border will be inside of the box e.g..box {width: 350px; border: 10px solid black;}leads to a box rendered in the browser ofwidth: 350px. The content box can't be negative and is floored to 0, making it impossible to use border-box to make the element disappear. - Here the dimension is calculated as, width = border + padding + width of the content, and height = border + padding + height of the content.
Formal syntax
content-box | border-box
Examples
/* support Firefox, Chrome, Safari, Opera, IE8+ and old Android */
.example {
-moz-box-sizing: border-box;
box-sizing: border-box;
}
Specifications
| Specification | Status | Comment |
|---|---|---|
| CSS Basic User Interface Module Level 3 The definition of 'box-sizing' in that specification. |
Candidate Recommendation | Initial definition |
Browser compatibility
| Feature | Chrome | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
|---|---|---|---|---|---|---|
| Basic support | 1.0 -webkit[1] 10.0 |
(Yes) | 1.0 (1.7 or earlier)-moz[1] 29.0 (29.0) |
8.0[1] |
7.0 | 3.0 (522)-webkit 5.1[2] |
| Feature | Android | Firefox Mobile (Gecko) | IE Phone | Opera Mobile | Safari Mobile |
|---|---|---|---|---|---|
| Basic support | 2.1-webkit[1] 4.0 |
1.0 (1.0)-moz [1] 29.0 (29.0) |
9.0 | (Yes) | (Yes) |
[1] box-sizing is not respected when the height is calculated from window.getComputedStyle(), in Internet Explorer (all versions), in Firefox prior to 23, and in Chrome. Edge doesn't exhibit the problem. Note that IE9's proprietary currentStyle property does return the correct value of height.
[2] The vendor prefix -webkit was removed in 534.12.