box-sizingBaseline · Widely available
The box-sizing CSS property sets whether an element's width and height are calculated based on the content-box, which does not count the size of borders or padding, or border-box, which does count them.
Supported in all major browsers for at least 30 months — safe to use without fallbacks. Baseline since Jul 29, 2015. Widely available since Jan 29, 2018.
Browser support
DesktopChrome
1–9Not supported
10+Supportedsince Mar 8, 2011
Current: 155Edge
12+Supportedsince Jul 29, 2015
Current: 154Firefox
1–28Not supported
29+Supportedsince Apr 29, 2014
Current: 157Safari
1–5Not supported
5.1+Supportedsince Jul 20, 2011
Current: 27MobileChrome Android
18+Supportedsince Jun 27, 2012
Current: 155Firefox Android
4–28Not supported
29+Supportedsince Apr 29, 2014
Current: 157Safari iOS
1–5Not supported
6+Supportedsince Sep 10, 2012
Current: 27How to use
This feature is Baseline widely available — use it freely, no fallback needed.
Example
Full syntax and examples are on MDN: box-sizing.
Feature detection
CSS · check before using
@supports (box-sizing: initial) {
/* styles that rely on box-sizing */
}
/* or in JavaScript */
if (CSS.supports("box-sizing", "initial")) {
// use it
}Documentation (MDN)
Specification
Usage share
Sub-features
Support for each part of the feature (3). The overall table above shows when the whole feature works.
| Sub-feature | Chrome | Edge | Firefox | Safari | Chrome Android | Firefox Android | Safari iOS |
|---|---|---|---|---|---|---|---|
| box-sizing | 10 | 12 | 29 | 5.1 | 18 | 29 | 6 |
| box-sizing.border-box | 10 | 12 | 29 | 5.1 | 18 | 29 | 6 |
| box-sizing.content-box | 10 | 12 | 29 | 5.1 | 18 | 29 | 6 |