This is an experimental technology
Because this technology's specification has not stabilized, check the compatibility table for usage 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 specification 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 |
| Animation type | discrete |
| 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 content, 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.
padding-box- The
widthandheightproperties include the content, the padding but neither the border, nor the margin. Only Firefox implemented this value, and it was removed in Firefox 50.
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) |
8.0[1] |
7.0 | 3.0 (522)-webkit 5.1[3] |
|
padding-box |
No support | No support | 1.0 (1.7 or earlier)-moz[1] 29.0 (29.0) Removed in 50.0 (50.0) |
No support | No support | No support |
| 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)[2] |
9.0 | (Yes) | (Yes) |
padding-box |
No support | 1.0 (1.0)-moz[1] 29.0 (29.0) Removed in 50.0 (50.0) |
No support | No support | No support |
[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] In addition to the unprefixed support, Gecko 44.0 (Firefox 44.0 / Thunderbird 44.0 / SeaMonkey 2.41) added support for a -webkit prefixed version of the property for web compatibility reasons behind the preference layout.css.prefixes.webkit, defaulting to false. Since Gecko 49.0 (Firefox 49.0 / Thunderbird 49.0 / SeaMonkey 2.46) the preference defaults to true.
[3] The vendor prefix -webkit was removed in 534.12.