Why does this assume 16px?

16px is the default root font size in every major browser unless a site explicitly overrides it on the element. If your project sets a different root size, scale the result accordingly.

PX to Rem Converter

Convert pixel values to rem units, live as you type, based on the standard 16px root font size.

100% private, runs in your browser

Pixels (px)

Rem

Assumes the default 16px root font size. Type in either field — the other updates live.

Need the opposite? Use Rem to PX Converter

What is PX to Rem Converter?

Convert a pixel value to the equivalent rem unit, assuming the standard 16px browser default root font size — the most common conversion needed when moving a CSS design from fixed px values to scalable rem units.

FAQ

16px is the default root font size in every major browser unless a site explicitly overrides it on the <html> element. If your project sets a different root size, scale the result accordingly.

rem units scale with the user's font-size preference and the page's root size, making layouts more accessible and easier to scale consistently.