PX Unit Calculator
Convert between px, rem, em, %, and pt using a custom base font size.
Tip: If your root font size is 16px, then 24px = 1.5rem.
What is a px calculator?
A px calculator helps you convert pixel values into other CSS units used in modern web design. While pixels are straightforward, responsive layouts often benefit from relative units like rem, em, and percentages. This tool gives you instant conversions so you can make cleaner design decisions without doing mental math every time.
In practical frontend work, designers and developers constantly translate spacing, font sizes, and component dimensions. A px calculator is especially useful when refactoring old fixed-width styles into scalable responsive systems.
Why px to rem conversion matters
1) Better accessibility
Using rem allows the interface to scale with the user's browser settings. If someone increases their default font size for readability, rem-based typography and spacing respond naturally.
2) Consistent design systems
Design systems usually define a base unit. Converting px values into rem keeps spacing and typography proportional across a product, even when base font size changes.
3) Easier responsive behavior
Relative units are easier to adapt across devices. Instead of rewriting dozens of pixel-based values at each breakpoint, rem and em units can reduce the amount of custom overrides.
Core formulas used by this calculator
- px to rem: rem = px ÷ base
- rem to px: px = rem × base
- px to em: em = px ÷ base (when base is parent font size)
- % to px: px = (percent ÷ 100) × base
- pt to px: px = pt × (96 ÷ 72)
Quick reference table (base 16px)
| Pixels (px) | Rem | Percent |
|---|---|---|
| 12px | 0.75rem | 75% |
| 14px | 0.875rem | 87.5% |
| 16px | 1rem | 100% |
| 18px | 1.125rem | 112.5% |
| 20px | 1.25rem | 125% |
| 24px | 1.5rem | 150% |
| 32px | 2rem | 200% |
Practical use cases
Converting a Figma handoff
Design files are commonly expressed in pixels. If your codebase uses rem, this calculator helps you translate those values quickly. For example, a 40px heading at base 16 becomes 2.5rem.
Building a spacing scale
Many teams define spacing tokens like 4px, 8px, 12px, 16px, and so on. You can convert each token to rem once and maintain consistent spacing across components.
Refactoring old CSS
Legacy CSS often hardcodes everything in px. Convert values section by section—typography first, then spacing, then component dimensions—to gradually modernize without breaking layouts.
Common mistakes to avoid
- Using the wrong base: rem uses root font size; em depends on parent context.
- Mixing units randomly: keep a clear strategy for typography, spacing, and breakpoints.
- Ignoring browser defaults: many environments use 16px, but not always.
- Over-precision: avoid long decimals when short values are visually identical.
Final thoughts
A good px calculator does one thing well: it removes friction from everyday CSS work. Whether you are translating design specs, tuning responsiveness, or improving accessibility, quick unit conversion helps you ship cleaner, more maintainable frontend code.
Use the converter above whenever you need fast, accurate values—and keep your CSS system consistent from the first component to the last.