CSS Unit Calculator
Convert between px, rem, em, vw, vh with live preview
Convert between CSS units with real-time preview and responsive breakpoints. Perfect for developers, designers, and AI-assisted workflows. No CSS expertise required - just enter values and get accurate conversions.
Live Preview
See results visually
AI-Friendly
Convert AI CSS outputs
Responsive
Multiple device sizes
Absolute pixels - fixed size regardless of context
Common Use Cases
Typography Scale
Common font sizes for web typography
Layout Spacing
Consistent spacing values for layouts
Responsive Sizing
Viewport-based responsive units
Rem vs Em
Use rem for consistent sizing relative to root font. Use em when you want sizing relative to parent element.
Viewport Units
vw/vh are perfect for responsive design. 100vw = full viewport width, 100vh = full viewport height.
AI Workflow
When AI gives you CSS in px, convert to rem for better accessibility and responsive behavior.
Responsive Design Examples
Mobile Hero Section
Full-height hero on mobile devices
iPhone
Typography Scale
Scalable text sizes using rem
Root font size
Container Width
Responsive container with max-width
Desktop
Perfect for Modern Builders
AI-Assisted Development
Perfect when AI tools like ChatGPT give you CSS in pixels but you need rem, em, or viewport units for better responsive design.
💡 Convert AI-generated CSS from px to rem for accessibility and responsive scaling
Responsive Web Development
Calculate and convert between units for responsive layouts, typography scales, and cross-device compatibility.
💡 Convert fixed pixel values to flexible viewport units for mobile-first design
Design System Implementation
Perfect for Webflow, Figma, or no-code builders who need to convert design tokens between different unit systems.
💡 Convert design system spacing from px to rem for consistent scaling across components
How CSS Unit Conversion Works
Understanding CSS Units
CSS units fall into two main categories: absolute units (like px, pt, cm) and relative units (like rem, em, vw, vh, %). Our calculator handles the math and context needed for accurate conversions.
Unit Categories & Best Practices
- Absolute units (px, pt, in): Fixed size regardless of context. Best for borders, shadows, and precise layouts.
- Relative units (rem, em): Scale with font size. Perfect for typography, spacing, and accessibility.
- Viewport units (vw, vh): Based on screen size. Ideal for responsive layouts and full-screen elements.
- Percentage (%): Relative to parent element. Great for flexible layouts and component sizing.
Why Use Our CSS Unit Calculator?
For Developers & Designers
Modern web development requires flexible, responsive designs. Our calculator eliminates guesswork when converting between CSS units, ensuring your layouts work perfectly across all devices and accessibility settings.
- Convert legacy pixel-based designs to responsive units
- Calculate viewport units for full-screen layouts
- Create accessible typography scales with rem
- Preview how changes affect visual appearance
- Ensure consistency across design systems
For AI Builders & No-Code Creators
AI tools often generate CSS in pixels, but modern responsive design requires relative units. Our calculator bridges this gap, making AI-generated code more accessible and responsive.
- Convert AI-generated px values to responsive rem/em
- Adapt designs for Webflow, Bubble, or Framer
- Create mobile-first layouts with viewport units
- Ensure accessibility compliance with relative units
- No CSS knowledge required - just copy and paste
💡 Pro Tips for CSS Unit Conversion
For AI Workflows:
When ChatGPT or Claude gives you CSS with pixel values, convert margin/padding to rem and widths/heights to vw/vh for better responsive behavior. Always test on multiple screen sizes.
For Accessibility:
Use rem for font sizes and spacing to respect user font size preferences. Avoid px for typography - screen readers and browser zoom work better with relative units.