Dev Tools
CSS Unit Converter
The CSS Unit Converter converts a length between pixels, em, rem, points, and percent, using a base font size you choose so the conversion matches your actual project setup. It's a quick reference for developers translating a design spec into CSS, or double-checking how a rem value compares to pixels at a particular root font size.
All the math runs instantly in your browser as you type, with nothing sent to a server — it's just a calculation happening locally on the numbers you enter.
How to Use the CSS Unit Converter
- Open the CSS Unit Converter tool.
- Enter the base font size you're working with.
- Type the value you want to convert and pick its unit.
- Read off the equivalent value in the other units.
Frequently Asked Questions
Why does rem depend on a base font size but em doesn't work the same way?
Rem is always relative to the root element's font size, while em is relative to the font size of the element it's used on, so the converter's base font size setting specifically models the rem and root-relative calculations.
What base font size should I use if I'm not sure?
16px is the default browser font size and a common baseline, so start there unless your project explicitly sets a different root font size.
Does this tool send my design values anywhere?
No, every conversion is a simple calculation done locally in your browser, with no data transmitted anywhere.