PX ↔ REM Converter | px to rem, rem to px
Convert between px and rem for responsive, accessible CSS. Set a custom base font size, batch-paste values, and copy CSS-ready output—everything runs locally in your browser.
How to Use This Tool
- 1
Select a mode: PX → REM or REM → PX.
- 2
Set the base font size (default: 16px) to match your project.
- 3
Paste single or multiple values (comma, space, or newline separated).
- 4
View live results or click Convert in Manual mode.
- 5
Copy CSS-ready output with comments or download as a file.
Use Cases & Examples
Responsive Web Design & Mobile-First
Translate design specs from px to rem so components scale smoothly across breakpoints.
Web Accessibility (WCAG)
Adopt rem for type and spacing to respect user preferences and improve WCAG compliance.
Design Tokens & Systematization
Batch-convert spacing and type scales to standardized rem tokens for maintainable design systems.
Fluid Typography & clamp()
Compute rem values for clamp() min/max to build fluid, scalable typography.
PX vs REM in CSS
px is an absolute CSS unit; rem is relative to the root (html) font-size.
With a 16px base, 1rem equals 16px. Changing the base scales all rem values uniformly.
Using rem improves accessibility and responsiveness by honoring user font-size preferences.
Frequently Asked Questions
Q.How do I set the correct base font size? What's the standard?
A. Most browsers default to 16px. Use your project’s root html font-size as the base (e.g., 16px, or 10px if using the 62.5% technique).
Q.When should I use px vs rem? Best practices for CSS units
A. Prefer rem for typography and spacing to respect user settings. Keep px for pixel-perfect details like hairlines, borders, and shadows.
Q.What's the calculation formula? Can I do reverse calculations?
A. Formulas: rem = px ÷ base; px = rem × base. Example: base 16px → 24px = 1.5rem.
Q.How does rem affect responsive design and mobile layouts?
A. Adjust the base font-size at breakpoints to scale all rem-based values consistently for responsive layouts and fluid type.
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