Free PX to REM Converter - CSS Unit Calculator 2026

Welcome to Code Formatter PX to REM Converter – the fastest, most intuitive online tool for converting between pixel and rem CSS units. Our professional-grade calculator instantly transforms pixels to rem and rem to pixels with support for custom base font sizes. Whether you're building responsive websites, implementing accessible typography, or modernizing legacy CSS, our converter makes unit translation effortless.

In modern web development, rem units have become the gold standard for scalable, accessible design. Unlike fixed pixels, rem values scale proportionally with the user's browser settings, ensuring your typography remains readable for users who adjust their default font size. Our converter helps you bridge the gap between pixel-based designs and rem-based implementations.

How to Use Our PX to REM Converter

Converting CSS units has never been simpler. Our real-time calculator provides instant results:

Enter Your Pixel Value: Type the pixel measurement from your design file (Figma, Sketch, Photoshop) into the left "Pixel Value" input field.
Adjust Base Font Size: If your project uses a non-standard base font size, update the "Base Font Size" field (default is 16px, the browser standard).
Get Instant Results: The converted rem value appears immediately in the right pane, along with ready-to-use CSS code.
Copy and Use: Click "Copy REM" to grab the value for your stylesheet, or copy the complete CSS property.

Understanding PX vs REM Units

Choosing the right CSS unit is crucial for building accessible, responsive websites:

Pixels (PX)

Pixels are absolute units that always render at the same physical size regardless of context. While predictable, they don't scale when users adjust their browser's default font size, potentially causing accessibility issues for users with visual impairments who rely on larger text settings.

Root EM (REM)

REM stands for "root em" and is a relative unit based on the root element's font size (typically the <html> element). By default, browsers set this to 16px. When a user changes their browser's font size setting, all rem-based measurements scale proportionally, maintaining your design's proportions while respecting user preferences.

The Conversion Formula

The mathematical relationship between pixels and rem is straightforward:

PX to REM: rem = px ÷ base-font-size
REM to PX: px = rem × base-font-size

With a standard 16px base: 24px ÷ 16 = 1.5rem, and 2rem × 16 = 32px.

Common PX to REM Conversions

Reference these frequently used conversions (assuming 16px base):

12px = 0.75rem – Small text, captions
14px = 0.875rem – Body text alternative
16px = 1rem – Default body text
18px = 1.125rem – Slightly larger body text
20px = 1.25rem – Subheadings
24px = 1.5rem – H3 headings
32px = 2rem – H2 headings
48px = 3rem – H1 headings

Why Use REM for Responsive Design?

Adopting rem units offers significant advantages for modern web development:

Accessibility Compliance: Respects user font size preferences, meeting WCAG 2.1 guidelines for resizable text.
Consistent Scaling: Change the root font size once to scale your entire site proportionally.
Easier Maintenance: Adjust global typography by modifying a single CSS variable.
Responsive Typography: Combine with media queries to adjust base size at different breakpoints.
Design System Friendly: Creates predictable, proportional spacing and sizing throughout your design system.

Frequently Asked Questions

What base font size should I use?

The browser default of 16px is recommended for most projects. This is what users expect and what accessibility guidelines assume. Only change it if you have a specific design requirement.

Should I use REM for everything?

Use rem for font sizes, spacing, and layout dimensions that should scale with text. Use pixels for borders, shadows, and decorative elements where you want fixed sizes. Media queries typically stay in pixels.

What's the difference between EM and REM?

EM is relative to the parent element's font size, which can lead to compounding issues with nested elements. REM is always relative to the root element, providing more predictable behavior across your entire site.

How do I set a custom base font size?

Add html { font-size: 18px; } to your CSS to change the base. Some developers use font-size: 62.5% (10px) for easier math, making 1.6rem equal to 16px.

Will REM work in all browsers?

Yes! REM units have excellent browser support, working in all modern browsers and back to IE9. There are no compatibility concerns for any current web project.

How do I convert an entire CSS file to REM?

Use our converter to calculate individual values, or use PostCSS plugins like "postcss-pxtorem" to automate the conversion during your build process.

Is 0.0625rem the same as 1px?

With a 16px base, yes: 1 ÷ 16 = 0.0625. However, for very small values like borders, using pixels directly (1px) is often clearer and more intentional in your code.

Can I use CSS variables with REM?

Absolutely! Defining --spacing-sm: 0.5rem in your CSS custom properties creates a powerful, scalable design token system that adapts to user preferences.