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PX to REM Converter — With Custom Root Font Size

Convert pixel values to rem units and back, with the root font size configurable rather than assuming the 16px browser default — important because rem is always relative to the html element's font-size, which a design system frequently sets differently.

How to use PX to REM

1. Set your root font size (default 16px, or your design system's value).
2. Enter a pixel or rem value.
3. Read the converted result.

Frequently asked questions

Why does rem depend on a root font size at all?

By definition, 1rem always equals the html element's computed font-size — if your project sets that to something other than the 16px browser default, every rem-to-px conversion shifts accordingly, which is why the root size must be configurable here.

Why use rem instead of px in CSS at all?

rem scales proportionally when a user changes their browser's base font size for accessibility, whereas a fixed px value ignores that preference entirely.

Can I convert several values at once?

Enter values one at a time for a precise conversion tied to your specific root font size setting.

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