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Convert between px, em, rem, %, pt, cm units.
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Among ToolsMonk's converters, CSS Unit Converter covers a single everyday need: convert between px, em, rem, %, pt, cm units. Open the page and start working, with no download or sign-up standing between you and the result.
This tool is especially useful for workflows such as converting a px value to rem for scalable, accessible sizing, translating designs from pixels into relative css units, and checking em vs rem values against a base font size. Because it runs directly in your browser, you can use it on desktop, tablet, or mobile while keeping the process fast and easy for one-off tasks as well as repeat work.
Everything about CSS Unit Converter is tuned for speed to first result, with privacy-friendly processing and the rest of ToolsMonk's tools nearby when the next task comes up.
| Price | Free, no signup, no paywall, no watermark |
|---|---|
| Works on | Any modern browser: desktop, tablet, and mobile |
| Processing | In your browser, files never leave your device |
| Account required | None |
| Category | Converters |
Enter a value and its unit (e.g. 24px)
Set the base/root font size (commonly 16px)
See the equivalent in rem, em, %, and other units
Copy the value for your CSS
Converts between CSS units, px, rem, em, %, and more
Set the base font size for accurate rem/em conversion
Instant results for responsive sizing
Helpful for consistent, scalable layouts
Runs in your browser, nothing is uploaded
Free, with no signup and no cap on conversions
Converting a px value to rem for scalable, accessible sizing
Translating designs from pixels into relative CSS units
Checking em vs rem values against a base font size
Building responsive, accessible layouts
CSS Unit Converter exists to make one job effortless: convert between px, em, rem, %, pt, cm units. Professionals, students, and one-time visitors all get the same instant, accurate results in the browser: no installation, no account, no waiting.
All processing runs locally in your browser, so your files and data never leave your device. Like every tool in the Converters collection, it works across all modern browsers on desktop, tablet, and mobile: same features, same results, on every device.
CSS Unit Converter translates between CSS units, px, rem, em, percentages and more, with a configurable base font size, helping you move from pixel-based designs to the relative units that make layouts scalable and accessible.
The core relationships matter: px is absolute, rem is relative to the root (html) font size, and em is relative to the parent element. Since browsers default the root to 16px, 1rem usually equals 16px, which is why the converter asks for a base, because changing the root size changes all the px↔rem maths.
Why convert to rem at all? Accessibility and scalability. rem respects a user's browser font-size preference and lets you rescale an entire design from one root value, whereas px is fixed and ignores user settings. em is useful for component-relative spacing but has a catch, it compounds through nesting, so deeply nested ems can produce surprising sizes, which is why rem is often preferred for predictability.
Conversion runs in your browser with nothing uploaded. Pair it with the Color Code Converter and other ToolsMonk developer tools for your front-end and design-to-code workflow.
Default the base to 16px (the browser default) unless your root font-size differs
Prefer rem for predictable, accessible sizing; reserve em for component-relative spacing
Remember em compounds through nesting, rem doesn't, which avoids surprises
Common questions about this tool, its workflow, and what to expect before you use it.
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Convert between px, em, rem, %, pt, cm units.
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