TestMu 2025 - The Largest Virtual Software Testing Conference is Back | 50,000+ Attendees

Next-Gen App & Browser
Testing Cloud

Trusted by 2 Mn+ QAs & Devs to accelerate their release cycles

Start free with Google Start free with Email

CSS3 Box-sizing

.css3-boxsizing is a property used to specify whether or not an element’s border and padding should be included in the element’s computed width, height and margin.

Last updated on : 2025-03-16

Browser Versions

Edge

Firefox

Chrome

Safari

Opera

5.5 - 7

8 - 11

12 - 133

2 - 138

4 - 136

3.2 - 18.4

9 - 9

9.5 - 114

Fully Supported

Partially

No Support

Formal Definition

Inherited

Applies to

all elements that accept width or height

Initial value

content-box

Animation type

discrete

Computed value

as specified

Specifications

CSS Box Sizing Module Level 3 # box-sizing

Syntax

box-sizing: border-box;
 box-sizing: content-box;
 /* Global values */
 box-sizing: inherit;
 box-sizing: initial;
 box-sizing: revert;
 box-sizing: unset;

Browser Compatibility

CSS3 Box-sizing on IE is fully supported on 8-11, and not supported on 5.5-7 IE versions.

CSS3 Box-sizing on Edge is fully supported on all Edge versions.

CSS3 Box-sizing on Firefox is fully supported on all Firefox versions.

CSS3 Box-sizing on Chrome is fully supported on all Chrome versions.

CSS3 Box-sizing on Safari is fully supported on all Safari versions.

CSS3 Box-sizing on Opera is fully supported on 9.5-114, and not supported on 9-9 Opera versions.

CSS3 Box-sizing on Safari on iOS is fully supported on all Safari on iOS versions.

CSS3 Box-sizing on Android Browser is fully supported on all Android Browser versions.

CSS3 Box-sizing on Opera Mobile is fully supported on all Opera Mobile versions.

CSS3 Box-sizing on Chrome for Android is fully supported on all Chrome for Android versions.

CSS3 Box-sizing on Firefox for Android is fully supported on all Firefox for Android versions.

CSS3 Box-sizing on Samsung Internet is fully supported on all Samsung Internet versions.

Browser Support for CSS3 Box-sizing

CSS3 Box-sizing on Chrome

CSS3 Box-sizing on Safari

CSS3 Box-sizing on Firefox

CSS3 Box-sizing on Internet Explorer

CSS3 Box-sizing on Opera

CSS3 Box-sizing on Edge

References

Data sourced from

100

High

Overall Browser Compatibility Score

Note:CSS3 Box-sizing shows a browser compatibility score of 100. This is a collective score out of 100 to represent browser support of a web technology. The higher this score is, the greater is the browser compatibility. The browser compatibility score is not a 100% reflection for every browser and the web technology support. However, it does give you an estimate on how much you should rely on a particular web technology in terms of browser compatibility.

Test on 3000+ browsers for CSS3 Box-sizing & more

Test your website for CSS3 Box-sizing and other web technologies. Get 100 FREE automation test minutes!

Test Now