coderef

rlh unitBaseline · Widely available

The rlh CSS length unit is a font-relative length relative to the line height of root element.

Supported in all major browsers for at least 30 months — safe to use without fallbacks. Baseline since Nov 21, 2023. Widely available since May 21, 2026.

How to use ↓Compare browsers

Browser support

DesktopChrome
1–110Not supported
111+Supportedsince Mar 7, 2023
Current: 155
Edge
12–110Not supported
111+Supportedsince Mar 13, 2023
Current: 154
Firefox
1–119Not supported
120+Supportedsince Nov 21, 2023
Current: 157
Safari
1–16.3Not supported
16.4+Supportedsince Mar 27, 2023
Current: 27
MobileChrome Android
18–110Not supported
111+Supportedsince Mar 7, 2023
Current: 155
Firefox Android
4–119Not supported
120+Supportedsince Nov 21, 2023
Current: 157
Safari iOS
1–16.3Not supported
16.4+Supportedsince Mar 27, 2023
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

There’s no simple runtime check for this feature; rely on the support table and test in your target browsers.

Specification