Convert CSS Units Online
Switch between px, rem, em, vw, vh and percentages
px | 16 | Absolute pixels — fixed, unaffected by user settings | |
em | 1 | Parent element font-size multiples — cascades with nesting | |
vw | 1.11111 | Percentage of viewport width | |
vh | 1.77778 | Percentage of viewport height | |
% | 100 | Percentage of parent element font-size |
Use this CSS Unit Converter to translate design and layout values between px, rem, em, vw, vh and percentage units. It helps frontend developers, UI designers, students and design-system teams convert Figma pixel values into scalable CSS, check responsive viewport units, calculate rem sizes from a base font size and compare layout values before writing code. CSS units are context-dependent, so the same number can behave differently depending on root font size, parent font size or viewport dimensions. This tool gives you a clearer conversion view before you add values to stylesheets, components or design tokens.
How to Convert CSS Units
Enter a value, pick a unit, set your context, and get all equivalents instantly.
Enter a value and unit
Type a numeric value into the input field and select the source unit from the dropdown: px, rem, em, vw, vh, or percent. The conversion table below updates immediately with the equivalent value in all other units.
Configure base font size and viewport
The conversion of rem, em, vw, and vh depends on context. Set your base font size (the root font-size in your CSS, commonly 16px or 10px) and your viewport width and height (the screen size you are designing for, such as 1440x900 for desktop or 375x812 for mobile). All conversions recalculate instantly when you adjust these settings.
Read the full conversion table
The output table shows your value in px, rem, em, vw, vh, percent width, and percent height simultaneously. This makes it easy to compare options — for example, to see whether 1.5rem or 24px better describes the same value in your design system, or to find the vw value that matches a specific pixel width on your target viewport.
Features
Converts values between px, rem, em, vw, vh and percentages
Calculates rem values from a configurable root font size
Compares em output against the selected font-size context
Translates viewport units using custom viewport width and height
Shows multiple CSS unit equivalents in one practical view
Helps convert Figma pixel values into scalable CSS units
Supports decimal values for precise spacing and typography work
Clarifies context-dependent units before implementation
Improves responsive design decisions for layouts and components
Reduces manual math mistakes when building CSS from designs
What This Tool Helps You Do
Convert CSS values between px, rem, em, vw, vh and percentages so design numbers are easier to use in real layouts. A value from a design file may be in pixels, but your frontend code may need rem for typography, vw for fluid sections or percentages for layout behavior.
This converter helps you compare those units before adding them to CSS.
Why CSS Unit Context Matters
CSS units are not always fixed. rem depends on the root font size. em depends on the current element font size. vw and vh depend on viewport dimensions. Percentages depend on the parent element. That means a conversion can be mathematically correct but still behave differently inside a component.
The practical decision is not only “what is 24px in rem?” but “which unit makes this layout easier to maintain?”
Practical Ways to Use This Tool
- Convert Figma pixel values into rem for scalable typography
- Translate fixed widths into vw for responsive sections
- Compare px and em values inside component styles
- Check spacing values before creating design tokens
- Estimate mobile and desktop viewport-based sizes
- Pair sizing decisions with a Color Contrast Checker when reviewing readable UI
- Use a Color Palette Generator when building a new design system
- Resize supporting visual assets with a Resize Image tool before adding them to layouts
What to Check Before Using a Value
Confirm the root font size used in your project. Many sites keep the browser default 16px, but some design systems change it. Also check whether the value belongs to text, spacing, layout width or viewport behavior. The best unit depends on where the value is used.
For responsive typography, consider clamp() when pure vw becomes too large on wide screens or too small on mobile.
Expert Tips
Use rem for predictable typography and spacing across components. Use em when a value should scale with the local component text size. Use px for precise borders, icons or small fixed details. Use viewport units carefully for hero sections, full-screen layouts and fluid sizing.
Do not convert every pixel value automatically. Choose units based on intent, not only arithmetic equivalence.
Common Mistakes to Avoid
- Assuming px to rem conversion works without checking root font size
- Using vw for font sizes without min and max limits
- Forgetting that em changes inside nested font-size contexts
- Expecting percentage height to work when parent height is undefined
- Copying desktop viewport conversions directly into mobile layouts
- Mixing too many unit types without a design-system reason
- Treating converted values as final without browser testing
- Using responsive units where fixed pixel precision is required
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Frequently Asked Questions
What does a CSS unit converter do?
A CSS unit converter changes a value from one CSS unit into equivalent values in other units. It is useful when moving between fixed pixel values and responsive units such as rem, em, vw or vh.
How do I convert px to rem?
Divide the pixel value by the root font size. For example, with a 16px root font size, 24px equals 1.5rem. If your project changes the root font size, the rem result changes too.
Can I use this for Figma to CSS conversion?
Yes. Designers often provide values in pixels, while developers may implement spacing and typography in rem or responsive units. This converter helps translate those values before coding.
Does em work the same as rem?
No. rem is based on the root font size, while em is based on the current element's font size. This makes rem more predictable for global sizing and em more context-sensitive inside components.
Is vw better than px for responsive layouts?
Not always. vw scales with viewport width, which is useful for fluid layouts, but it can become too small or too large without limits. Many production layouts combine relative units with min, max or clamp rules.
Why does percentage height behave differently from percentage width?
Percentage width usually depends on the parent width. Percentage height needs the parent height to be defined clearly, otherwise the result may not behave as expected.
When should I use rem instead of px?
Use rem when you want spacing or typography to scale from a consistent root size. Use px when you need fixed pixel precision, such as borders, exact icons or certain image dimensions.
What viewport size should I enter?
Use the viewport width and height that match the design or device you are testing. For example, a desktop design, tablet layout and mobile screen can produce different vw and vh values.
Can this help with responsive typography?
Yes. It can help compare px, rem and viewport-based sizes before you decide on a typography rule. For production, test the result across small and large screens.
What should I check before using converted values?
Check the project's root font size, component font context, target viewport and accessibility behavior. A mathematically correct conversion may still need visual testing in the real layout.
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