What is the default base font size?

Browsers default to 16px. So 1rem = 16px unless you change the root font size.

Why use rem instead of px?

rem units scale with the user's font size preference, making your site more accessible. They also make it easier to maintain consistent spacing.

Set font-size on the html element. For example, html { font-size: 62.5%; } makes 1rem = 10px for easier math.

Convert between CSS px and rem units. Set a custom base font size. Free online converter.

Base font size (px)

PX to REM

REM to PX

Reference table (base: 16px)

Convert pixel values to rem and back. Set a custom base font size for accurate conversion. Essential for responsive CSS development.

Bidirectional

Convert px → rem or rem → px.

Custom base

Set any base font size (default 16px).

Quick reference table

Common px values and their rem equivalents.