Why CSS units matter
Pixels (px) are absolute, while rem and em are relative to font sizes, making layouts more accessible and scalable. This tool assumes the common 16px default root font size for rem conversions.
CSS Unit Converter
Enter a value and choose units to convert instantly between px, rem, em, and pt.
How it works
- 1
Fill in the form fields the tool shows.
- 2
Change modes or toggles if available.
- 3
Copy the generated output when it looks right (often updates live).
Why use this tool
- Runs entirely in your browser — nothing is uploaded to a server.
- 100% free, no sign-up, no limits.
- Works in any modern browser — no app install, no extension, no account.
How to use CSS Unit Converter
Complete the fields in CSS Unit Converter. Output is produced in your browser from those inputs — copy it when ready.
Tips for better results
Empty optional fields if you want a minimal result. Invalid combinations should surface an error message.
Privacy and offline-friendly processing
Whenever possible, CSS Unit Converter processes your data locally with JavaScript in this page. That means drafts, secrets, and unfinished work stay on your device by default. Prefer this workflow when you do not want to upload sensitive text, tokens, passwords, or files to a third-party service.
Frequently asked questions
What base font size does this use?
It assumes the standard 16px default browser font size, which is the typical baseline for rem calculations.
What is the difference between rem and em?
rem is always relative to the root font size, while em is relative to the parent element’s font size, which can compound in nested elements.
Is my data uploaded when I use this tool?
For most FlyUtils tools, no. Processing happens in your browser with JavaScript. If a tool ever needs a server, that will be stated clearly on the page.
Is CSS Unit Converter free to use?
Yes. CSS Unit Converter is free, with no sign-up and no artificial usage caps for normal personal and work use.
Does CSS Unit Converter work on mobile?
Yes. The page is mobile-first, so you can paste input, tweak options, and copy results from a phone or tablet.