About EM to REM Conversion
EM and REM are both relative CSS units, but they scale differently. EM is relative to its parent element's font size, while REM is relative to the root (html) element's font size. This converter helps you translate between these units.
How to Use This Tool
- Enter the EM value you want to convert
- Specify the parent element's font size in pixels
- Specify the root element's font size in pixels
- Click "Convert to REM" to get the equivalent REM value
- Copy the result and use it in your CSS
The Conversion Formula
The formula to convert EM to REM is:
rem = (em × parent-font-size) / root-font-size
For example, to convert 1.5em to rem when parent is 14px and root is 16px:
(1.5 × 14) / 16 = 1.3125rem
Why Convert Between EM and REM?
- Consistency: REM provides more predictable sizing across components
- Accessibility: REM units scale better with user preferences
- Maintenance: Easier to manage global sizing changes
- Component Development: When creating reusable components
Key Differences Between EM and REM
- EM is relative to its parent element's font size
- REM is always relative to the root element's font size
- EM values compound in nested elements
- REM values remain consistent regardless of nesting
- EM is better for local scaling, REM for global consistency
Best Practices
- Use REM for most global sizing (typography, spacing)
- Use EM for components that should scale with their context
- Be mindful of compounding effects with nested EM values
- Set your root font size in pixels for predictable REM values
- Document your unit strategy for team consistency