PX to REM: The CSS Unit Conversion That Scales
Hardcoding px in CSS breaks accessibility. Here's why rem is better — and a free converter to make the switch.
# PX to REM Converter: CSS Unit Conversion Made Easy
The rem unit is the foundation of accessible, responsive CSS. But converting between pixels and rem in your head gets old fast — especially when your project uses a non-standard root font size. FreeToolJet's PX to REM Converter does the math instantly, with a quick reference table and one-click CSS copying.
The Formula
rem = px ÷ root font size
With the default browser root size of 16px: 24px = 1.5rem, 32px = 2rem, and so on.
Why Use rem Instead of px?
- Accessibility: rem respects the user's browser font-size setting. If someone increases their default from 16px to 20px, all your rem-based sizes scale proportionally.
- Consistency: rem creates a predictable scaling system. Set
font-size: 1remon the body and use multiples throughout. - Responsive design: rem-based spacing and typography scale naturally across viewports.
When to Still Use px
- Borders (
border: 1px solid) - Box shadows and fine decorative details
- Canvas and SVG coordinates
Quick Reference (base: 16px)
| Pixels | REM |
|---|---|
| 10px | 0.625rem |
| 12px | 0.75rem |
| 14px | 0.875rem |
| 16px | 1rem |
| 20px | 1.25rem |
| 24px | 1.5rem |
| 32px | 2rem |
| 48px | 3rem |
| 64px | 4rem |
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## Why Use rem Instead of px
The rem unit is relative to the root font size (the <html> element). By default, browsers set the root font size to 16px, so 1rem = 16px. Using rem has several advantages:
- Accessibility: Users who increase their browser font size get proportionally larger text. With
px, text stays the same size regardless of user preference. - Scalability: Change one variable (root font size) and all rem-based sizes scale proportionally. This is useful for responsive design.
- Consistency:
remvalues create a consistent spacing scale.0.5rem, 0.75rem, 1rem, 1.5rem, 2remis a natural typographic scale.
The 62.5% Trick
A common technique is to set the root font size to 62.5%:
html { font-size: 62.5%; } /* 1rem = 10px */
body { font-size: 1.6rem; } /* 16px */This makes 1rem = 10px, so 1.6rem = 16px, 2.4rem = 24px, etc. The math is easy because you just multiply by 10. However, this technique has a downside: it overrides the user font size preference. Use it with caution on accessibility-sensitive projects.
When to Use px vs rem vs em
- px: Borders, hairline separators, and fixed UI elements that should not scale with font size.
- rem: Font sizes, padding, margin, and most spacing. Scales with user preferences.
- em: Spacing relative to the current element font size. Useful for components that should scale internally (e.g., a button whose padding scales with its text size).