CSS REM Calculator
Convert pixels to rem and convert rem values back to pixels. Use this while building responsive interfaces and design systems. rem relates to the root element’s font size; actual display still depends on browser styles and zoom.
Use the tool
Enter your values, then run it. The result is generated in your browser.
Result
Calculated
How to use CSS REM Calculator
- Confirm the computed root font size.
- Convert design tokens with that value.
- Test layouts under different viewport and user font settings.
Formula and assumptions
rem = pixels ÷ root font size. Pixels = rem × root font size.
Unit conversion does not predict all CSS rendering behavior.
Frequently asked questions
Is 1rem always 16px?
Only if the root element’s computed font size is 16 CSS pixels.
How is em different?
em is generally relative to the current element’s font size; rem uses the root font size.
Should every value use rem?
Choose units based on the property and accessibility behavior you need.
About this tool
Use this while building responsive interfaces and design systems. rem relates to the root element’s font size; actual display still depends on browser styles and zoom.
No account is required. The tool runs in this browser and this starter build has no form-submission backend. See the method and assumptions before relying on estimates.