PX to REM Converter — Free Tool

What Is a PX to REM Converter?

This tool converts between pixel (px) and rem units instantly. Rem units are the foundation of accessible, responsive CSS — they scale proportionally when users adjust their browser's default font size, while pixel values stay fixed. Converting your CSS from px to rem improves accessibility for millions of users with low vision.

The Conversion Formula

The formula is simple: rem = px ÷ base font size. With the default base of 16px, 24px = 1.5rem. This tool includes an adjustable base size, a full reference table, and a bulk converter that transforms all px values in a CSS block to rem at once.

How to Use This PX To Rem

Enter a pixel value — Type the pixel size you want to convert — common values include 12, 14, 16, 18, 20, 24, 32, 48px.
Set the base font size — The default is 16px (browser standard). Change this if your project uses a different root font size.
Read the rem value — The tool instantly shows the equivalent rem value. For example, 24px ÷ 16 = 1.5rem.
Use the reference table — The built-in conversion table shows common px-to-rem mappings for quick reference.

Tips and Best Practices

→ Use rem for scalable designs. Rem values scale with the user's browser font-size setting, making your design accessible to users who've increased their default text size.
→ Keep px for borders and shadows. Thin lines (1px borders, small shadows) should stay in pixels. A 0.0625rem border doesn't scale usefully and can render inconsistently.
→ Don't change the root font size. Avoid setting html { font-size: 62.5% } to make 1rem = 10px. It breaks user preferences and causes accessibility issues. Keep the default 16px and do the math.
→ Combine rem with CSS clamp(). Use clamp(1rem, 2.5vw, 2rem) for fluid typography that respects both viewport size and user font preferences.

Frequently Asked Questions

What is the difference between px and rem?

Pixels are fixed units that stay the same size regardless of user settings. Rem units are relative to the root font size — if the user changes their browser's default font size, rem-based layouts scale proportionally, making them more accessible.

Why should I use rem instead of px?

Rem units respect user accessibility preferences. If a user sets their browser font size to 20px, rem-based text scales up. Pixel values ignore this, which can make content unreadable for users with low vision.

What is the default root font size?

The default root font size in all major browsers is 16px, meaning 1rem = 16px. You can change it with html { font-size: 18px; } to make 1rem = 18px, adjusting all rem values site-wide.

What is the formula for px to rem?+

Divide the pixel value by the root font size: rem = px ÷ root-font-size. With the default 16px root, 24px ÷ 16 = 1.5rem. With a 20px root, 24px ÷ 20 = 1.2rem.

Why should I use rem instead of px?+

Rem values respect the user's browser font-size preference (set in browser settings for accessibility). If a user increases their default font size from 16px to 20px, all rem-based sizes scale proportionally. Pixel values ignore this preference, creating accessibility barriers for users with visual impairments.

What is the difference between rem and em?+

Rem is relative to the root element (html) font size — always consistent. Em is relative to the parent element's font size — it compounds when nested. If a 1.5em element is inside another 1.5em element, the inner text is 2.25× the base size. Rem avoids this compounding problem.

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Built by Derek Giordano · Part of Ultimate Design Tools

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