About this tool
Convert any pixel value to rem (and rem back to pixels) against a configurable root font size — 16px by default, since that is what browsers ship with. A reference table of common sizes (12–48px) is generated for your chosen base.
rem units scale with the user's root font-size setting, which is why accessibility guidance prefers them over fixed pixels for typography: a user who bumps their browser's default text size actually gets bigger text. The mental math is just division by 16, but a converter removes the friction that tempts developers back to hard-coded px.
How to use it
- Set your root font size if it differs from 16px.
- Type a px value (or a rem value for the reverse direction).
- Copy the converted unit; use the reference table for common sizes.
Frequently asked questions
What is the difference between rem and em?
rem is relative to the root element's font size — stable and predictable. em is relative to the current element's font size, so nested em values compound.
Why is 16px the default base?
Every major browser ships with a 16px default root font size, making it the universal reference point unless a stylesheet overrides it.
Should I use rem for everything?
Typography and spacing benefit most. Borders and hairlines are often better in px, since scaling a 1px border to 1.25px just blurs it.