CSS layouts often mix pixel, rem, em, and percentage units, and converting between them by hand means remembering the base font size and doing the division correctly every time. This tool handles that instantly.
Set your root font size (16px is the browser default unless your CSS overrides it), then convert any value between px, rem, em, and percent — all relative to that same base size.
This is useful when translating a design mockup's pixel measurements into rem for accessible, scalable CSS, or checking what a percentage-based value actually equals in pixels for a specific base size.
Because everything runs locally in your browser, results appear instantly and nothing you type or upload is ever sent to a server.
Bookmark this page if you expect to use this tool regularly — it loads fast and behaves the same way every time, with no account needed.
This kind of task shows up constantly in everyday writing, coding, design, and admin work, which is exactly why a dedicated, focused tool saves so much back-and-forth.
A tool that does one job well, without a cluttered interface or unrelated features competing for attention, tends to be faster to use than a heavier all-in-one app.
If you find yourself needing this conversion or calculation often, keeping this page open in a tab is usually faster than digging through a bigger software suite's menus.
Frequently asked questions
What's the difference between rem and em?
rem is always relative to the root (html) element's font size, while em is relative to the current element's own font size, which can compound in nested elements.
Why use rem instead of px?
rem values scale properly when a user changes their browser's default font size for accessibility, while fixed px values don't respond to that setting.