Advanced PX to REM Converter
Free Online Tool
Use our Advanced PX to REM Converter to convert pixel values to REM or vice versa with precision. Designed for modern web developers and software testers. This free tool offers bidirectional conversion, custom root font sizing, and batch CSS processing all with accessibility and responsive design in mind.
- Testsigma
- Free online Tools
- PX to REM Converter
Convert Pixels to REM
Enter pixel value to convert to REM units
Quick Reference Table
Common conversions • Base: 16px
| Pixels | REM | Use Case |
|---|---|---|
| 8px | 0.50rem | Small icons, fine print |
| 12px | 0.75rem | Caption text |
| 14px | 0.88rem | Small body text |
| 16px | 1.00rem | Body text (default) |
| 18px | 1.13rem | Large body text |
| 20px | 1.25rem | Small headings |
| 24px | 1.50rem | Subheadings |
| 32px | 2.00rem | Medium headings |
| 48px | 3.00rem | Large headings |
| 64px | 4.00rem | Display text |
What is the PX to REM Converter?
Understanding PX and REM Units
In web design, PX (pixels) and REM (root em) are two of the most common CSS units used to define dimensions, spacing, and typography. Understanding the distinction between them is critical for creating scalable, responsive interfaces that adapt seamlessly to different devices.
Pixels (px) are fixed units representing a single dot on a display. They are absolute and do not scale based on user preferences or screen settings.
For instance:
font-size: 16px;
margin: 20px;These values will remain constant, regardless of the user's browser zoom level or root font size. While this offers predictability, it can hinder accessibility and responsiveness.
REM (root em), on the other hand, is a relative unit based on the root element's font size - typically set in the <html> tag.
For example:
html {
font-size: 16px;
}
p {
font-size: 1.5rem; /* equals 24px */
}This makes REM units ideal for responsive design since changing the root font size proportionally affects all REM-based values. This is especially beneficial for users who increase their browser's default font size for better readability.
Why Use REM Over PX
Using REM units promotes scalability, accessibility, and design consistency across screen sizes and resolutions. Unlike pixels, REM units adjust dynamically, ensuring that elements remain legible and proportionate.
Advantages of using REM:
- Accessibility: Complies with WCAG 2.1/2.2 guidelines by allowing text scaling for visually impaired users.
- Responsive Design: Adapts smoothly across mobile, tablet, and desktop devices.
- Maintainability: Updating one root font size can globally resize all elements.
- Framework Compatibility: Supported by all major frameworks like Bootstrap 5, Tailwind CSS, and Material UI.
Ultimately, converting PX to REM helps designers and developers create fluid, user-centered interfaces that perform well across devices and align with accessibility standards.
Advanced Features of PX to REM Converter
The Advanced PX to REM Converter isn't just another calculator - it's a professional-grade tool built for developers, designers, and teams aiming for pixel-perfect, responsive web interfaces. With powerful conversion logic and developer-friendly controls, it delivers both speed and precision.
Bidirectional Conversion
Convert PX → REM and REM → PX instantly. Whether you're modernizing legacy CSS or verifying responsive scales, bidirectional support ensures flexibility.
Example:
/* Input */
font-size: 32px;
/* Output */
font-size: 2rem; /* assuming base 16px */You can also reverse the process:
font-size: 2rem; /* Input */
font-size: 32px; /* Output */This dual conversion flow helps both frontend developers and UI designers test and optimize scaling consistency across platforms.
Custom Root Font Size
By default, most browsers use a root font size of 16px. However, many design systems and frameworks adopt different bases like 18px or 20px to improve visual hierarchy.
This converter allows you to:
- Define a custom base font size.
- Automatically update all conversions.
- Save preferred configurations for future use.
For instance:
html {
font-size: 18px;
}Then 18px / 18 = 1rem. This flexibility ensures consistent scaling across multiple projects and frameworks.
Bulk CSS Block Conversion
Tired of converting values line by line? The bulk CSS block converter processes entire style sheets in seconds.
Paste your CSS block, select a root base, and get a converted version with clean, accurate REM values.
Example:
/* Input */
body {
margin: 24px;
padding: 16px;
font-size: 18px;
}
/* Output */
body {
margin: 1.5rem;
padding: 1rem;
font-size: 1.125rem;
}This batch feature is perfect for developers refactoring old codebases or enforcing responsive typography systems.
Live Responsive Preview Panel
Experience real-time scaling with the Live Responsive Preview Panel. As you modify font sizes or change the root base, the panel dynamically updates, showcasing:
- How text and layout respond to scaling.
- WCAG-compliant contrast and sizing metrics.
- Device viewport previews (mobile, tablet, desktop).
This instant visual feedback helps designers validate scaling decisions before deployment.
Multi-Base Conversion Tables
Switch between different bases (16px, 18px, 20px) effortlessly. The multi-base conversion table displays equivalent REM and PX values side-by-side for reference.
| PX | REM (16px) | REM (18px) | REM (20px) |
|---|---|---|---|
| 8px | 0.5rem | 0.44rem | 0.4rem |
| 16px | 1rem | 0.89rem | 0.8rem |
| 32px | 2rem | 1.78rem | 1.6rem |
This ensures quick comparison across multiple scaling systems - ideal for design teams using different frameworks or base settings.
Copy and Share Functionality
Once your conversions are ready, copy them directly or share via a generated link. Collaboration-ready features make it easy to share results with teammates, clients, or stakeholders.
- One-click copy: Copy converted CSS instantly.
- Shareable links: Send results without exporting files.
- Version-safe storage: Each conversion session retains settings and context.
These advanced features position this converter as one of the most comprehensive and user-friendly tools available online.
How to Use the PX to REM Converter?
Single Value Conversion
For quick conversions:
- Enter a value in PX (e.g., 32px).
- Set your base font size (default: 16px).
- Instantly get the REM equivalent.
Formula:
rem = px / baseExample:
32px / 16 = 2remBatch Conversion Tutorial
To convert multiple CSS properties at once:
- Paste your CSS code block.
- Choose a conversion direction (PX → REM or REM → PX).
- Adjust the base font size.
- Click Convert - results are displayed instantly.
Batch conversion saves hours of manual work when refactoring legacy projects.
Using Preview Feature
The preview window shows how converted values affect live text or UI components. You can test font scaling and spacing behavior under different resolutions.
Preview modes:
- Mobile View: 375px viewport.
- Tablet View: 768px viewport.
- Desktop View: 1440px viewport.
This helps you validate responsive typography visually.
Custom Root Fonts
Not every project uses the browser default. To customize root fonts:
- Go to Settings → Root Font Size.
- Choose or enter your preferred base (e.g., 18px).
- All conversions update automatically.
html {
font-size: 18px;
}A flexible base ensures accurate scaling across all devices and design systems.
Conversion Tables
16px Base Table
| PX | REM |
|---|---|
| 8px | 0.5rem |
| 12px | 0.75rem |
| 16px | 1rem |
| 20px | 1.25rem |
| 24px | 1.5rem |
18px Base Table
| PX | REM |
|---|---|
| 9px | 0.5rem |
| 18px | 1rem |
| 27px | 1.5rem |
| 36px | 2rem |
| 45px | 2.5rem |
20px Base Table
| PX | REM |
|---|---|
| 10px | 0.5rem |
| 20px | 1rem |
| 30px | 1.5rem |
| 40px | 2rem |
| 50px | 2.5rem |
These tables serve as quick references when designing or coding responsive layouts.
Best Practices PX to REM Converter
When to Use REM vs PX
Use REM for typography, spacing, and layout elements that should scale with accessibility preferences. Use PX for fine-grained control on borders, shadows, or images.
Rule of thumb:
- Use REM for font-size, margin, padding, layout widths.
- Use PX for borders, icons, and precise alignment.
Accessibility Benefits
REM units directly support WCAG 2.1/2.2 standards. When users increase browser zoom, REM-based text and components scale uniformly, ensuring readability for all.
This promotes inclusive design and improves user experience across devices.
Design System Integration
Frameworks like Tailwind CSS and Bootstrap 5 rely heavily on REM for consistency and scalability.
Example (Tailwind):
text-lg { font-size: 1.125rem; }
text-xl { font-size: 1.25rem; }By maintaining REM-based spacing and typography, teams ensure a cohesive look throughout the system.
Browser Compatibility
REM units are supported by 99%+ browsers, including Chrome, Firefox, Safari, and Edge. They degrade gracefully on legacy browsers, ensuring safe implementation even in mixed environments.
Professional Use Cases of PX to REM Converter
Legacy Code Conversion
Migrating old pixel-based code? The converter instantly refactors entire CSS files into scalable REM-based syntax, modernizing outdated design systems.
Design-to-Code Workflow
Designers using tools like Figma or Adobe XD can export pixel specs and convert them to REM before handing off to developers - ensuring accurate scaling in production.
Typography Scales
Create proportional font hierarchies using consistent REM ratios:
| Level | Size | REM |
|---|---|---|
| h1 | 48px | 3rem |
| h2 | 36px | 2.25rem |
| h3 | 24px | 1.5rem |
| body | 16px | 1rem |
Responsive Testing
During QA, testers can use the converter to simulate scaling behaviors, ensuring that typography and spacing remain consistent across breakpoints.
Understanding the Formula
PX to REM Formula
rem = px / baseIf your base font size is 16px:
32px / 16 = 2remREM to PX Formula
px = rem × baseExample:
1.25rem × 16 = 20pxCommon Examples
| PX | REM (16px base) |
|---|---|
| 8px | 0.5rem |
| 16px | 1rem |
| 24px | 1.5rem |
| 32px | 2rem |
| 40px | 2.5rem |
Benefits of Testsigma’s PX to REM Converter
Time Savings
Automate repetitive conversions and streamline workflows. Convert hundreds of properties in seconds, saving hours of manual labor.
Accessibility Compliance
Ensure every font and spacing value complies with WCAG 2.1/2.2 standards - critical for enterprise and public-facing applications.
Team Collaboration
With copy & share functionality, teams can maintain consistent scaling across multiple contributors, minimizing design drift.
Visual Testing
Integrated previews enable side-by-side comparison of PX and REM outputs, ensuring that responsive layouts behave as intended across all viewports.
Final Thoughts
The Advanced PX to REM Converter is not just a calculator - it's a comprehensive responsive design assistant. It empowers developers, designers, and teams to create scalable, accessible, and visually consistent interfaces with precision and efficiency.
Whether you're optimizing a legacy project, building a new design system, or ensuring accessibility compliance, this converter is your go-to professional tool for modern CSS transformation.
Frequently Asked Questions
What is a PX to REM converter and why do I need one?
How do I convert PX to REM using this tool?
It’s straightforward:
- Set your root font size (defaults to 16px).
- Pick a mode: PX→REM or REM→PX.
- Enter your value.
- Get the result instantly and hit Copy.
For a batch: paste a CSS block into the bulk area and convert everything in one go
Can I convert multiple PX values at once with batch conversion?
Yes. Paste a snippet, a full stylesheet segment, or a list of values (comma or newline separated) into the bulk field, click Convert Batch, and you’ll get clean, formatted results for all of them. It’s ideal for legacy refactors and token migrations.
What is the difference between PX and REM units in CSS?
- PX are fixed units; 16px stays 16px no matter the user’s settings.
- REM are relative to the root
<html>font size (usually 16px). If a user bumps their default type size, REM-based UI scales with it.
Use REM for typography and spacing; use PX for borders, hairlines, and pixel-critical details.
How does the responsive preview panel work?
Can I use a custom root font size instead of the default 16px?
Is REM better than PX for web accessibility?
How do I integrate REM units with design systems like Bootstrap or Tailwind CSS?
Both Bootstrap 5 and Tailwind CSS use REM-based scales. Convert your values with the tool, then:
- Put them into design tokens or CSS variables, or
- Update your Tailwind config (e.g., theme.fontSize, theme.spacing) to use the converted REM values.
This keeps your spacing and typography consistent across components.
