CSS px ↔ rem Converter
Convert between CSS units px and rem.
px (Pixels)
An absolute unit that represents one pixel on the screen. Has a fixed size and is limited for responsive design.
rem (Root EM)
A relative unit based on the font size of the root element (html). Beneficial for accessibility and responsive design.
Conversion Formula
Usage Recommendations
- • Font size: rem recommended
- • Spacing (margin, padding): rem recommended
- • Border: px usable
- • Media queries: rem recommended
Complete CSS Unit Guide
Choosing the right CSS units in web development greatly affects user experience and accessibility. Learn the differences between px and rem and how to use them in appropriate situations.
📐 Features
- • Absolute unit with 1:1 correspondence to screen pixels
- • Consistent size across all browsers
- • Precise layout control possible
- • Not affected by user settings
✅ Recommended Use Cases
- • Border thickness (1px, 2px)
- • Shadow offset
- • Icon sizes (16px, 24px)
- • Fine spacing adjustments
⚠️ Cautions
- • Ignores user font size settings
- • May cause accessibility issues
- • Limited for responsive design
📐 Features
- • Based on root element (html) font size
- • Reflects user settings
- • Maintains consistent proportions
- • Accessibility-friendly
✅ Recommended Use Cases
- • Font size settings
- • Spacing (margin, padding)
- • Container sizes
- • Media query breakpoints
💡 Advantages
- • Maintains proportions when scaling
- • Improves accessibility
- • Easy maintenance
🎯 Unit-specific Usage Strategy
Typography
Use rem for font sizes and line spacing rem
Layout
Use rem for spacing and containers rem
Details
Use px for borders and shadows px
📱 Responsive Design Tips
Mobile-first Approach
Set base font size to 16px and scale with rem units
html { font-size: 16px; }
h1 { font-size: 2rem; /* 32px */ }Media Query Usage
Maintain consistency with rem-based breakpoints
@media (min-width: 48rem) { /* 768px */ }
html { font-size: 18px; }
}♿ Accessibility Considerations
✅ Recommended Practices
- • Set font sizes with rem units
- • Maintain minimum font size of 16px
- • Sufficient line spacing (1.5 or more)
- • Minimum touch target of 44px
❌ Things to Avoid
- • Using fixed px values for font sizes
- • Small text below 12px
- • Fixed container widths
- • Line spacing of 1.0 or less
🔧 Browser Support and Compatibility
px Unit
Perfect support in all browsers. Available from IE6+.
rem Unit
Perfect support in IE9+ and modern browsers. Fallback needed for IE8 and below.
For IE8 support: Declare px value first, then add rem value as fallback
font-size: 18px; /* IE8 fallback */
font-size: 1.125rem; /* Modern browsers */