Free CSS Unit Converter - px to rem, em, pt, vh, vw Converter
Convert between px, rem, em, pt, vh, vw, and other CSS units instantly. Perfect for responsive design and accessibility.
What is CSS Unit Converter?
Our CSS Unit Converter helps you convert between all CSS units: px (pixels), rem (root em), em (relative to parent), pt (points), vh (viewport height), vw (viewport width), %, and more. Essential for building responsive websites, ensuring accessibility, and converting between design specs and code.
Different CSS units serve different purposes. Pixels (px) are absolute and simple but bad for accessibility. Rem and em scale with font size, making text accessible for users who adjust browser font settings. Viewport units (vh, vw) scale with screen size, perfect for responsive layouts. Our tool converts between all these with customizable base font sizes.
The tool includes real-time conversion as you type, configurable base font size (default 16px), viewport dimensions for vh/vw calculations, and generates copy-ready CSS code. You can also see multiple unit equivalents simultaneously, helping you choose the best unit for your use case.
All conversions are calculated locally in your browser using standard CSS formulas. No server requests, instant results, and perfect for offline use. Works great for converting entire stylesheets or individual values.
Powerful Features
Everything you need in one amazing tool
All CSS Units
Convert px, rem, em, pt, vh, vw, %, cm, in, mm. All CSS units supported.
Custom Base Size
Set custom base font size (default 16px). Get accurate conversions for your project.
Responsive Units
Calculate vh, vw based on viewport dimensions. Perfect for responsive design.
Real-Time Conversion
See conversions as you type. Instant feedback for all units.
Bulk Conversion
Convert multiple values at once. Paste list of values and get all conversions.
CSS Code Generate
Copy-ready CSS code with converted values. Paste directly into stylesheets.
How It Works
Get started in 4 easy steps
Enter Value & Unit
Type value with unit (e.g., 16px, 1rem). Or select from dropdown.
Set Base Font Size
Configure base font size (typically 16px). Affects rem and em calculations.
See All Conversions
Tool shows equivalent values in all units. Real-time updates as you adjust.
Copy Unit
Copy converted value to clipboard. Use in CSS, documentation, or design specs.
Why Choose Our CSS Unit Converter?
Stand out from the competition
Accessibility First
Convert to rem/em for better accessibility. Respect user font size preferences.
Instant Results
Convert units in real-time. No delays or processing time.
Responsive Design
vh/vw calculations for fluid layouts. Build truly responsive interfaces.
CSS Code Ready
Generate valid CSS code with converted units. Copy-paste into projects.
Unlimited Conversions
Convert as many units as needed. No limits or restrictions.
100% Private
All conversions local. Your design specs and CSS stay private.
Perfect For
See how others are using this tool
Design to Code
Convert Figma/Sketch px values to rem/em for accessible CSS implementation.
Accessibility Compliance
Ensure WCAG compliance by using relative units that scale with user preferences.
Responsive Layouts
Use vh/vw for fluid typography and spacing that scales with viewport.
Stylesheet Migration
Convert entire stylesheets from px to rem for better maintainability.
Typography Systems
Build consistent typography scales using rem-based modular scales.
Cross-Browser Testing
Test how different units render across browsers and user font settings.
Frequently Asked Questions
Everything you need to know about CSS Unit Converter
Both are relative units, but they have different reference points. "rem" (root em) is always relative to the root <html> element's font size (typically 16px). "em" is relative to the parent element's font size, which can compound and become confusing. If you set font-size: 2em on an element inside another 2em element, it becomes 4× the base size. Rem avoids this cascading problem. Use rem for predictable, consistent sizing throughout your site.
Using rem respects user accessibility preferences. Users with vision impairments often increase their browser's default font size (via Settings → Font Size). With px, your text stays the same size regardless. With rem, your entire layout scales proportionally with the user's preference. This is required for WCAG accessibility compliance. Additionally, rem makes it easier to build consistent design systems - change the root font size and everything scales together.
vh (viewport height) and vw (viewport width) are percentage units based on viewport size. 1vh = 1% of viewport height, 100vh = full viewport height. They're perfect for full-screen sections, fluid typography (font-size: calc(1rem + 1vw)), and maintaining aspect ratios. Unlike %, which is relative to parent, vh/vw is always relative to the viewport. Great for responsive design but be careful on mobile where address bars can affect viewport height.
Most browsers default to 16px, so that's the standard. In your CSS, set html { font-size: 100%; } which respects user preferences rather than forcing a value. Then use rem throughout your stylesheet. Common pattern: 1rem = 16px, 0.875rem = 14px, 1.25rem = 20px. Some developers use html { font-size: 62.5%; } to make 1rem = 10px for easier math, but this breaks if users set a different base size.
Yes! You can and should use different units for different purposes. Use rem/em for font sizes and spacing to support user preferences. Use px for borders, box-shadows (1px border should always be 1 pixel). Use % for widths in grid layouts. Use vh/vw for full-height sections. Use ch (character width) for limiting text line length. Modern CSS calc() lets you combine units: calc(100vh - 60px) or calc(1rem + 2px).
The conversions use standard CSS formulas and are mathematically accurate. However, actual rendering depends on browser, OS, display settings, and user preferences. For example, rem conversions assume a 16px base font size by default, but users may have changed this in their browser settings. Viewport unit conversions depend on actual viewport dimensions. Always test your CSS in real browsers and devices, especially for critical layouts and typography.
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