CSS Unit Converter

Convert px, em, rem, %, vw and more CSS units with a custom base font size.

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Quick Answer

CSS Unit Converter is a free browser-based developer utility that validates, converts and formats developer data instantly, with no install and no server upload.

What Is CSS Unit Converter?

CSS Unit Converter is a free online developer tools tool that convert px, em, rem, %, vw and more css units with a custom base font size. Convert px, em, rem, %, vw and more css units with a custom base font size. This free online developer tool processes everything in your browser for privacy and speed. Unlike many similar tools, it runs entirely in your browser — no data is sent to any server, no account is required, and there are no usage limits. Whether you are a developer, writer, SEO professional, or casual user, this tool provides instant, accurate results without friction.

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How to Use CSS Unit Converter

Enter a value and choose the source and target units (px, em, rem, %, vw, vh). Set a base font size if you use em or rem. For more detail, read Testrefy's guides: CSS Flexbox Guide and CSS Grid Layout Guide..

Key Features

px, em, rem, %, vw, vh
Configurable base font
Instant conversion

Common Use Cases

Making fixed layouts responsive
Matching design system units
Scaling typography

Common Mistakes to Avoid

Forgetting em is relative to parent
Wrong base font size
Mixing vw and vh

Common Questions About CSS Unit Converter

Is it safe to paste secret keys or code?

Yes. Because all processing is client-side, pasted secrets and code never leave your device.

Best Practices for CSS Unit Converter

To get the most out of CSS Unit Converter, follow these best practices. Ensure your input data is clean and properly formatted for the most accurate results. Use the copy function to transfer output directly to your clipboard. Bookmark the tool for easy access. Check the related tools section below for complementary utilities that can enhance your workflow. Remember that all processing is client-side, so your data never leaves your browser.

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Privacy & Security

CSS Unit Converter processes all data entirely within your browser using JavaScript. No text, files, or personal information is transmitted to any server. Your data stays on your device, making this tool safe for sensitive content. We do not track usage, store inputs, or share data with third parties. The tool works offline after the initial page load and requires no account to use.

Frequently Asked Questions

Find answers to common questions about this tool.

What is the difference between em and rem?

em is relative to the parent element font size. rem is relative to the root (html) element font size. The CSS Unit Converter defaults to a 16px base but you can adjust it.

How do I convert px to rem?

Divide the px value by the base font size (default 16px). For example, 32px divided by 16px equals 2rem. Adjust the base size in the CSS Unit Converter to match your design system.

What are vw and vh units?

vw (viewport width) equals 1 percent of the browser window width. vh (viewport height) equals 1 percent of the window height. Use them for full-screen layouts and responsive typography.

What base font size should I use for rem calculations?

The browser default is 16px, which most frameworks like Tailwind and Bootstrap use. If your project sets a different base font size on the html element, adjust the base in the converter to match.

Can I convert between absolute and relative units?

Select the source and target unit. The converter shows the result based on your chosen base font size. For example, converting cm to rem requires knowing the physical pixel density and base size.

Resources

Topic Cluster

Regex tester, HTML entity encoder, number base converter, CSS unit converter, cron builder, UUID generator, timestamp converter, and HEX/RGB color converter for developers.

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8 tools in this topic

About Testrefy

All tools run entirely in your browser. No data is sent to any server. 100% private and free.

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