About REM to Percentage Conversion
This tool converts REM units (relative to root font size) to percentage units (relative to parent element size). Both are relative units but work differently in CSS layouts.
How to Use This Tool
- Enter the REM value you want to convert
- Specify the root font size in pixels (default is 16px)
- Specify the parent element size in pixels (default is 100px)
- Click "Convert to Percentage" to get the equivalent % value
- Copy the result and use it in your CSS
The Conversion Formula
The formula to convert REM to percentage is:
percentage = (rem × root-font-size) / parent-size × 100%
For example, to convert 1.5rem to percentage when root is 16px and parent is 200px:
(1.5 × 16) / 200 × 100% = 12%
Why Convert REM to Percentage?
- Fluid Layouts: When you need elements to scale with their container
- Responsive Design: For components that should adapt to different contexts
- Legacy Support: When working with older code that uses percentages
- Precise Control: When you need exact proportional relationships
Key Differences Between REM and Percentage
- REM is relative to the root element's font size
- Percentage is relative to the parent element's size
- REM provides consistent sizing throughout the document
- Percentage allows for fluid scaling within containers
- Percentage is often better for width/height, REM for typography
Best Practices
- Use REM for typography and global spacing
- Use percentage for fluid layouts and container-relative sizing
- Combine with max/min values to prevent extreme scaling
- Test your conversions at different viewport sizes
- Document your unit strategy for team consistency