Published 2026-02-02 · 1 min read
PX vs REM: Which Should You Use?
PX is measurable; REM respects user scaling. Here is a nuanced decision framework for beginners and design-system stewards alike.
Practical defaults
Use REM for typography, whitespace, radii tied to typography, and most component sizing. Reach for PX only when aligning to device pixels buys a crisp edge you cannot express another way.
Designer handoff
When stakeholders hand you pixel mocks, annotate the assumed root (html { font-size: 16px; }). Then derive REM with PX to REM and stash values in tokens.
Explore EM when padding should feel “attached” to nearby type—PX to EM preserves the maths.
Continue your reading order with Modern CSS units guide for 2026 once the REM habit sticks.
Frequently asked questions
- Can marketing stay in px?
- Briefs may be px, but code should converge on REM tokens. Convert intentionally, not implicitly.