Em to Rem Converter
Convert em units to rem units (and back) using parent and root font sizes.
Use the Em to Rem Converter
Em to Rem Converter
Result
1.0000 rem
Formula: rem = em × (parent px ÷ root px)
Reverse: Rem to Em
Result
1.0000 em
Formula: em = rem × (root px ÷ parent px)
Reference Table
Common conversions at 16px parent / 16px root (1em = 1rem at these defaults).
| Em | Rem (16px/16px) | Pixels |
|---|
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Summary
Em and rem are both relative CSS units, but they anchor to different elements. Em is relative to the font size of the parent element; rem is relative to the root (html) element font size. This converter lets you input an em value along with the parent and root font sizes to get the exact rem equivalent — and vice versa.
How it works
- Enter the em value you want to convert.
- Set the parent element font size in pixels (default 16px).
- Set the root (html) element font size in pixels (default 16px).
- The converter calculates: rem = em × (parent_px / root_px).
- Use the reverse section to convert rem back to em.
Use cases
- Convert a component's em-based spacing to rem for a design system with a non-default root font size.
- Check whether an em value from a third-party stylesheet is equivalent to its rem counterpart.
- Migrate legacy CSS that uses em throughout to a rem-first architecture.
- Verify that nested em values behave as expected relative to the document root.
Frequently Asked Questions
Last updated: 2026-07-14 · Reviewed by Nham Vu