PX to REM Converter
Convert pixel values to REM units for responsive design with configurable root font sizes and real-time preview. Perfect for scalable typography and mobile-first design with instant calculations and CSS output generation.
REM is relative to the root font size (html element)
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What is PX to REM Converter?
The PX to REM Converter transforms pixel measurements into REM units relative to a configurable root font size. The default root font size is 16px, matching the browser default. The formula is rem = px / rootFontSize. REM units provide consistent, predictable scaling because they always reference the root element, unlike EM which inherits from parent elements. All processing happens in your browser.
How does PX to REM Converter work?
REM (root EM) is a CSS unit that is always relative to the font size of the html root element. This tool divides the pixel value by the root font size to produce the REM equivalent. You can adjust the root font size to match your project configuration.
Key Features
- Configurable root font size
- Quick presets (14, 16, 18, 20px)
- Real-time conversion
- Copy result to clipboard
- Shows both px and rem values
- Runs in the browser with no uploads
- Bidirectional: rem to px too
- High precision output
Common Use Cases
Responsive web design
Convert pixel font sizes and spacing to REM units so the entire UI scales when users change their browser font size.
Accessibility improvements
Use REM units for font sizes so text respects user preferences for larger or smaller base text.
Design system tokens
Define spacing and typography tokens in REM units for a design system that scales uniformly.
Global font size changes
Change the root font size once and have all REM-based measurements update proportionally.
How to Use This Tool
Enter pixel value
Type the pixel measurement you want to convert.
Set root font size
Choose or enter the root font size (default is 16px).
View the result
The REM equivalent is displayed instantly.
Copy the value
Copy the converted REM value for use in your CSS.
Pro Tips
- 1
16px is the default root font size in most browsers.
- 2
REM always references the html element font size, never a parent.
- 3
Use REM for font sizes, spacing, and layout to respect user accessibility settings.
- 4
A root font size of 10px makes REM math simpler (1.6rem = 16px).
Frequently Asked Questions
What is the difference between REM and EM?
REM is always relative to the root html element font size. EM is relative to the parent element font size, which can cause compounding in nested elements.
Is my data sent to a server?
No. All conversion happens locally in your browser. Nothing is transmitted.
Why use REM instead of pixels?
REM units scale with the user browser font size setting, improving accessibility. Pixels are fixed and ignore user preferences for larger text.
Can I convert REM back to pixels?
Yes. The tool supports bidirectional conversion. Enter the REM value and root font size to get the pixel equivalent.
What root font size should I use?
Use 16px to match the browser default. Some teams use 10px or 62.5% to simplify mental math (1rem = 10px).