PX vs REM vs EM in CSS
Comparing CSS units for web typography and layout. Which is best for accessibility and responsive design?
When to use which?
Typography and Global Spacing
"Setting font sizes, margins, and padding across a web application."
Component-Level Scaling
"Building a button component that needs to scale its internal padding perfectly based on its own font size."
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Frequently Asked Questions
Q.Why should I stop using PX for fonts?
If you set a font size to 16px, it is hardcoded. If a user changes their browser default font size to 24px for accessibility reasons, your 16px text will not change, breaking accessibility.
Q.What is the default browser font size?
In almost all modern browsers, the default root font size is 16px. Therefore, 1rem = 16px by default.
Recommended Developer Utilities
Free, private, client-side tools relevant to this guide.
PX to REM Converter
The PX to REM Converter is an essential responsive design utility for modern web developers committed to accessibility standards. Hardcoding layout dimensions and typography in static pixels (px) prevents web browsers from scaling text properly for visually impaired users. Converting your design system to Relative EM (REM) units ensures that your entire interface scales dynamically based on the user's root browser font size preference. This zero-latency calculator allows you to define your project's root HTML font size and instantly perform bidirectional conversions between Pixels and REMs. Whether you are translating Figma mockups into Tailwind CSS config files or building responsive typography scales, this offline tool guarantees mathematical precision.
CSS Unit Converter
Convert between pixels, rem, em, and viewport units instantly. Essential for building accessible, fluid, and responsive web interfaces based on modern CSS standards.