CSS REM Converter
All-in-One Unit Calculator
Convert CSS units instantly. Type in REM or PX and automatically calculate EM, VW, VH, PT, Inches, CM, MM, PC, and Percentage. Perfect for responsive design, typography scales, and cross-device development. Customizable base font size and viewport dimensions with localStorage persistence. 100% client-side - your settings stay private.
Unit Converter
Root element font size units
Absolute pixel units
Common REM Values
| REM | PX (16px base) | EM | Common Use |
|---|---|---|---|
| 0.5rem | 8px | 0.5em | Extra small spacing |
| 0.75rem | 12px | 0.75em | Small text, captions |
| 0.875rem | 14px | 0.875em | Secondary text |
| 1rem | 16px | 1em | Body text (default) |
| 1.125rem | 18px | 1.125em | Large body text |
| 1.25rem | 20px | 1.25em | H5 heading |
| 1.5rem | 24px | 1.5em | H4 heading |
| 2rem | 32px | 2em | H3 heading |
| 2.5rem | 40px | 2.5em | H2 heading |
| 3rem | 48px | 3em | H1 heading |
EM vs REM: What's the Difference?
REM (Root EM)
Relative to the root element (usually <html>) font size.
font-size: 1.5rem; /* Always 24px if root is 16px */
EM
Relative to the parent element font size. Cascades through nested elements.
font-size: 1.5em; /* 24px if parent is 16px */
When to Use Each
- Global typography scales
- Layout spacing and margins
- Media query breakpoints
- Accessibility (respects user preferences)
- Component-specific scaling
- Padding relative to font size
- Button and icon sizing
- Self-contained modules
Frequently Asked Questions
Why We Built This REM Converter
Modern responsive web design requires developers to work with multiple CSS units - REM, EM, pixels, viewport units, and print measurements. However, mentally converting between these units while maintaining consistent typography scales is error-prone and time-consuming. Most online REM converters only support basic REM-to-PX conversion, leaving developers without tools to understand how their responsive typography translates to viewport units for truly fluid design, or to print measurements for PDF generation and printing. This comprehensive CSS REM converter was created to solve this problem by providing instant conversion between all major CSS units, customizable base font sizes and viewport dimensions, adjustable decimal precision, and localStorage persistence - all while processing everything client-side in your browser for complete privacy. Whether you are building typography scales, debugging responsive layouts, or creating print stylesheets, this tool provides the flexibility and accuracy you need.
Our REM calculator fills a critical gap in the responsive design workflow. Understanding the relationship between REM units and viewport units (vw, vh) is essential for creating truly fluid typography that scales proportionally with screen size - a technique used by modern design systems like Material Design and Tailwind CSS. Knowing how REM translates to print units (points, inches, picas) is crucial when generating PDFs or preparing web content for print. With live calculation as you type, preset buttons for common values, one-click copy functionality, and a comprehensive reference table of common typography scales, this is the most complete free REM conversion tool available. The advanced options panel lets you customize base font size (supporting non-standard bases like 10px or 14px), viewport dimensions (with presets for mobile, tablet, laptop, and desktop), and decimal precision (0-6 decimals for exact calculations). Every setting persists in localStorage, so your workflow preferences are remembered across sessions.
Beyond simple unit conversion, this tool educates developers on CSS unit best practices through comprehensive EM vs REM comparisons, real-world use case examples, and detailed FAQ documentation. Understanding when to use REM (global consistency, accessibility) versus EM (component scaling) versus pixels (precise borders) can dramatically improve code maintainability and user experience. Knowing that 1rem respects user browser font size preferences (accessibility) while 16px does not can be the difference between an inclusive website and one that fails WCAG guidelines. RJL.io is committed to building developer tools that not only solve immediate problems but also teach best practices - and this all-in-one CSS unit converter exemplifies that mission by combining powerful functionality with educational content to make developers more effective at building accessible, responsive, and maintainable websites.