Developer Tools

REM Calculator

Convert between rem and px units. Calculate root-relative font sizes for consistent, accessible typography.

Use REM Calculator to get instant results without uploads or sign-ups. Everything runs securely in your browser for fast, reliable output.

Your results will appear here.

Ready to run.

About this tool

REM units are relative to the root (html) element font-size, not parent. More predictable than em units, better for consistent spacing and typography.

If root is 16px: 1rem = 16px, 2rem = 32px, 0.5rem = 8px. Respects user browser settings for accessibility. Modern CSS best practice.

Usage examples

Consistent Heading

Same size everywhere

Root 16px: font-size: 2rem; = 32px

Spacing System

Rem-based spacing

margin: 1rem 2rem; = 16px 32px

How to use

  1. Enter "Root Font Size" (html element, default 16px).
  2. Enter "REM Value" to convert to pixels.
  3. Or enter "Pixel Value" to convert to rem.
  4. Click "Calculate" to see conversions.

Benefits

  • Convert rem to pixels
  • Convert pixels to rem
  • Root-relative sizing
  • No cascading issues
  • Accessible design
  • Consistent scaling

FAQs

What is REM in CSS?

rem (Root EM) is relative to root element (html) font-size, typically 16px. Unlike em (relative to parent), rem doesn't cascade. 1rem is same everywhere regardless of nesting. More predictable than em. Modern standard for typography.

Why use rem instead of pixels?

Benefits: respects user browser font-size settings (accessibility), scalable design system, easier maintenance (change root size scales everything), WCAG compliant. Pixels ignore user preferences. Rem allows users to zoom text properly.

What should I set as root font size?

Keep html { font-size: 100%; } (respects browser default, usually 16px). Avoid 62.5% trick - breaks accessibility. If you want different base, use font-size: 18px; on body. Root should stay 100% for user preferences.

Can I use rem for everything?

Use rem for: font sizes, padding, margin, most spacing. Use pixels for: borders (1px), box-shadows, small details, icons. Use % for: widths, responsive layouts. Use viewport units for: full-screen sections, fluid typography. Mix as needed!

How do I convert pixels to rem?

Formula: rem = px ÷ root font-size. If root is 16px: 24px = 24 ÷ 16 = 1.5rem, 12px = 0.75rem, 32px = 2rem. For 10px base (html: 62.5%): 24px = 2.4rem. Use calculator to avoid math errors.

What is browser support for rem?

rem supported in all modern browsers (IE9+). If supporting IE8, provide pixel fallback: font-size: 16px; font-size: 1rem; Older browsers use px, modern ones use rem. Safe to use rem in 2024+ without fallbacks.

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