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CSS Unit Converter (PX, REM, EM)

Convert CSS units instantly between px, rem, and em with configurable root and context font sizes. Includes formula breakdowns, scale tables, and copy-ready CSS output.

How to use this tool

  1. Enter a value and choose source/target units for conversion.
  2. Set root font size for rem and context font size for em accuracy.
  3. Copy the converted value, CSS declaration, or generated token snippet.

Unit selection guidance

  • Use px for fixed-size details like borders and hairlines.
  • Use rem for global spacing and typography that scales from root settings.
  • Use em for component-local scaling relative to inherited font size.

Workflow usage

  • Convert legacy pixel scales into rem-based design tokens.
  • Generate quick reference tables for common spacing values.
  • Audit mixed-unit stylesheets and standardize to a consistent approach.

FAQ

How do I convert px to rem?
Divide pixel value by the root font size. Example: 24px at 16px root becomes 1.5rem.
Why does em differ from rem?
rem is based on root font size, while em is based on the current element's computed font size.
Can I use this for spacing properties too?
Yes. The same conversions apply to margin, padding, gap, width, and related length properties.

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