CSS Unit Converter

CSS sizing

Convert pixels into rem, em, vw, and vh values using your chosen root font size and viewport.

Pixels

Root font size

Viewport width

Viewport height

rem1remem1emvw1.1111vwvh1.7778vh

font-size: 1rem;
width: 1.1111vw;
height: 1.7778vh;

Usage guide

Compare px, rem, em, vw, and vh using explicit assumptions

CSS length units respond to different reference values. Pixels are fixed CSS units, rem depends on the root font size, em depends on the current element context, and viewport units depend on the viewport dimensions.

How to use CSS Unit Converter

1.Enter the source value and the root font size or viewport dimensions used by your design.
2.Compare the converted values while remembering that em can depend on a local font-size context not captured by a global conversion.
3.Test the result in the real responsive layout rather than assuming mathematically equivalent values behave identically.

Examples

16 px equals 1 rem when the root font size is 16 px.
32 px equals 2 rem under the same 16 px root assumption.
50 vw represents half of the viewport width, so its pixel size changes with the browser width.

Limitations and notes

Browser zoom, user font settings, container layout, and inherited font sizes can change how units feel in practice.
A conversion can preserve a size at one viewport width without preserving responsive behavior at other sizes.

Should I use rem instead of px everywhere?

No single unit is best for every property. rem is useful for scalable typography and spacing, while px, percentages, viewport units, and container-relative units each have appropriate uses.

Why is em harder to convert?

em is relative to the font size of the current element or its context, so the reference value can differ across components.

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How the css unit converter works

Paste or enter the code, data, or value you want to inspect.

The tool processes it locally in your browser.

Copy the formatted output or converted value for your project.

Frequently Asked Questions

Is the css unit converter free?

Yes. It is free and does not require an account.

Is my code sent to a server?

No. These developer tools run locally in your browser.

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