coderef

remBaseline · Widely available

The rem CSS length unit is a font-relative length that is equal to the font size of the root HTML element which for most browsers is 16px.

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.

How to use ↓Compare browsers

Browser support

DesktopChrome
1–3Not supported
4+Supportedsince Jan 25, 2010
Current: 155
Edge
12+Supportedsince Jul 29, 2015
Current: 154
Firefox
1–3.5Not supported
3.6+Supportedsince Jan 21, 2010
Current: 157
Safari
1–4Not supported
5+Supportedsince Jun 7, 2010
Current: 27
MobileChrome Android
18+Supportedsince Jun 27, 2012
Current: 155
Firefox Android
4+Supportedsince Mar 29, 2011
Current: 157
Safari iOS
1–3.2Not supported
4+Supportedsince Jun 21, 2010
Current: 27

How to use

This feature is Baseline widely available — use it freely, no fallback needed.

Example

Full syntax and examples are on MDN — see the links below.

Feature detection

CSS · check before using
@supports (width: rem(5px, 2px)) {
  /* styles that use rem */
}

/* or in JavaScript */
if (CSS.supports("width", "rem(5px, 2px)")) {
  // use it
}

Specification

Usage share