box-sizing property CSS Reference

Definition and Usage

The box-sizing CSS property is used to alter the default CSS box model used to calculate widths and heights of 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 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


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


This 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.
The width and height properties include the padding size, and do not include the border or margin.
The 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.


/* support Firefox, WebKit, Opera and IE8+ */
.example {
  -moz-box-sizing: border-box;
       box-sizing: border-box;


Desktop browsers

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 1.0-webkit
1.0 (1.0)-moz


7.0 3.0 (522)-webkit
padding-box Not supported 1.0 (1.0) NA Not supported NA

Mobile browsers

Feature Android Firefox Mobile (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support 2.1-webkit
1.0 (1.0)-moz Mango 7.5 (Yes) (Yes)
padding-box NA 1.0 (1.0) NA NA NA

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