What does this tool do?
This px↔rem converter instantly turns pixel values into rem and em units (and back), with a root font size (base) you can adjust to match your project. It is built for CSS developers and designers creating accessible, scalable interfaces.
How to use it
- Adjust the values and options.
- See the result in the live preview.
- Copy the generated CSS/code into your project.
Why use rem instead of px?
The rem unit scales relative to the root element's font size, which defaults to 16px. When you define sizes in rem, your whole interface grows proportionally if a user increases their browser's font setting—a big win for accessibility. With this tool you can switch the base from 16 to 14 or 18 and watch every conversion shift instantly, so you can pick the scale that fits your design system.
Quick reference table and the em difference
The tool lists common sizes from 4px to 128px as rem and em for your chosen base, ready to copy straight into your CSS. rem is always tied to the root font size, while em is calculated against the nearest parent's font size. That's why the numeric values match in this table, but in a real project em can compound across nested elements and produce different results.
Frequently asked questions
Why is the default root font size 16px?
Nearly all browsers apply a default of 16px to the html element, so 1rem = 16px. This baseline holds unless the user changes their settings.
What's the difference between rem and em?
rem is always relative to the root (html) font size; em is relative to the nearest parent's font size and can compound in nested structures.
Is it a problem to use fractional rem values after changing the base?
No. With an 18px base, values like 24px = 1.3333rem are perfectly valid; browsers handle fractional rem values without issue.
Is px ↔ rem Converter free?
Yes. px ↔ rem Converter and all 300+ tools on MagmaNex are completely free with no signup or account required.
Is my data safe?
Yes. Everything runs locally in your browser. The data you enter is never sent to a server, stored, or shared.
Does it work on mobile?
Yes. px ↔ rem Converter works on phones, tablets and desktops — no app download needed.
🔒 Privacy: everything runs in your browser, your data is never sent to a server.