What is REM?
REM (Root EM) is a CSS unit that is relative to the font size of the root html element. Unlike pixels, which are fixed-size units, REM values scale proportionally with the user's browser settings. Most browsers default to a 16px root font size, so 1rem equals 16px by default. If a user increases their browser font size for accessibility, all REM-based measurements scale accordingly. This makes REM the preferred unit for building responsive, accessible web designs that respect user preferences.
How to Use This Tool
Enter a pixel value in the left input field, and the tool instantly calculates the equivalent REM value. You can also type a REM value on the right side to convert back to pixels. Adjust the base font size if your project uses a value other than the default 16px. The common conversions grid below provides a quick reference for frequently used sizes. Click any conversion to populate the input fields.
Common Use Cases
- Converting pixel values from design mockups to REM for CSS stylesheets
- Building accessible layouts that scale with user font size preferences
- Creating consistent spacing and typography scales in CSS or Tailwind projects
- Quickly referencing common pixel-to-REM conversions during development
Why Use a Client-Side Tool?
This converter runs entirely in your browser with no external dependencies. Calculations happen instantly as you type, with no network requests and no server involvement. Your values stay completely private. The tool works offline and is designed to fit seamlessly into your development workflow, providing a faster alternative to manual division or searching for conversion tables.
Frequently Asked Questions
What is the difference between px, em, and rem in CSS?
Pixels (px) are absolute units that stay the same size regardless of context. Em is relative to the parent element's font size, which can compound when nested. Rem is relative only to the root element font size, making it predictable and consistent throughout your entire document.
What base font size should I use?
The default browser base font size is 16px, and most CSS frameworks assume this value. Unless you have a specific design reason to change it, keeping the base at 16px ensures the best compatibility with browser defaults and user preferences.
Does changing the base font size affect all rem values?
Yes. Since rem is relative to the root font size, changing the base on the html element will scale every rem-based measurement proportionally. This lets you adjust your entire layout by modifying a single value.