What Are Pixels?
Pixels (px) are the most straightforward CSS unit - they represent exactly what you see on screen. When you set font-size: 16px, you're telling the browser to render text exactly 16 pixels high. This absolute unit provides precise control and has been the go-to choice for web developers for years.
However, pixels have a significant limitation: they're rigid and don't scale when users change their browser's default font size. This can create accessibility issues for users who need larger text to read comfortably.
Understanding REMs
REM (Root EM) units are relative units that scale based on the root element's font size (typically the <html> tag). By default, 1rem equals 16 pixels in most browsers. The key difference is that rem values adjust automatically when users change their browser's font size settings.
For example, if a user increases their browser's font size to 20 pixels, all rem-based measurements will scale proportionally. This makes rems an excellent choice for creating accessible, user-friendly designs.
Key Benefits of Using REMs
While pixels offer precise control, REMs provide several significant advantages that make them the preferred choice for modern web development:
Accessibility First
REMs respect user preferences by automatically scaling with browser font size settings. This makes your website more accessible to users with visual impairments or those who simply prefer larger text.
Consistent Scaling
When you adjust the root font size, all REM-based measurements scale proportionally. This ensures your layout maintains its visual harmony across different screen sizes and zoom levels.
Easier Maintenance
Need to adjust all font sizes? With REMs, you only need to change the root font size. This centralized control makes maintaining and updating your styles much more efficient than adjusting individual pixel values.
Better Responsive Design
REMs work seamlessly with media queries and responsive layouts. You can adjust the root font size at different breakpoints, and all REM-based measurements will adapt automatically.
When to Use Each Unit
While REMs offer many advantages, pixels still have their place in modern web development. Here's a practical guide for when to use each:
Use REMs for:
- Font sizes
- Padding and margins
- Width and height when they should scale with text
- Media query breakpoints
- Container sizing that should be responsive
Use Pixels for:
- Border widths
- Box shadows
- Fine details that shouldn't scale
- Image dimensions
- Fixed-size UI elements
Best Practices for Using REMs
To make the most of REM units, follow these proven best practices that will help you create more maintainable and accessible websites:
Start with the Default Root Size
Keep your root font size at 16px unless you have a compelling reason to change it. This aligns with browser defaults and user expectations. Remember: 1rem = 16px is a standard that users are accustomed to.
Use a Consistent Scale
Establish a clear scale for your REM values. For example: 0.75rem for small text, 1rem for body text, 1.25rem for larger text, and so on. This creates visual harmony and makes your code more predictable.
Document Your Conversions
Keep a reference of your pixel-to-REM conversions. Using CSS custom properties (variables) can help maintain consistency across your stylesheets and make updates easier.
Common Pitfalls to Avoid
Mixing Units Inconsistently
One of the biggest mistakes is mixing REMs and pixels without a clear strategy. Choose your units deliberately and stick to your system. If you're using REMs for spacing, use them consistently throughout your layout.
Overriding User Preferences
Using pixels for font sizes effectively disables the user's ability to scale text through browser settings. This is particularly problematic for accessibility and should be avoided.
Complex Calculations
Avoid complex mathematical operations with REM values. If you find yourself doing a lot of calculations, consider simplifying your approach or using CSS custom properties to manage values more effectively.
Pro Tip: When converting an existing project from pixels to REMs, use a conversion tool (like ours!) to ensure accuracy and consistency. This helps avoid common calculation errors and saves significant time.
Conclusion: Making the Switch to REMs
The debate between REMs and pixels ultimately comes down to creating websites that are both beautiful and accessible. While pixels offer precision, REMs provide the flexibility and scalability needed in modern web development. By understanding when to use each unit, you can create designs that look great and work well for all users.
Remember that switching to REMs doesn't mean abandoning pixels entirely. Instead, it's about making thoughtful choices that prioritize user experience and maintainability. Start small by converting your typography to REMs, then gradually expand to spacing and layout elements as you become more comfortable with relative units.
Ready to Start Using REMs?
Converting between pixels and REMs doesn't have to be complicated. Use our free converter tool to make the transition easier and ensure accurate conversions every time.
Try Our REM Converter Tool