PX to REM Converter

PX to REM Formula

rem = px / root-font-size

To convert pixels (px) to rem, divide the pixel value by the root font-size.

The table below shows common px to rem conversions based on the default browser root font-size of 16px. Use it as a quick reference when converting pixel values into scalable rem units.

Why Use REM Instead of PX?

REM units are preferred over pixels because they scale based on the root font-size. This makes your design more accessible, responsive, and more consistent across different devices.

When users adjust their browser's default font-size for readability, measurements defined in rem automatically adapt, while fixed pixel values do not. This results in better accessibility and a more flexible layout.

• Improved accessibility: resizes automatically for users with custom font-size settings.
• Consistent scaling: spacing, typography, and UI elements stay proportional.
• Responsive design: easier to maintain across different screen sizes.
• Cleaner code: fewer fixed pixel values in your CSS.

Best Practices for Using REM

Using <code>rem</code> units helps maintain scalable and consistent typography and spacing across your CSS. Below are the most reliable best practices for working with rem in modern frontend development.

• Set a clear root font-size: keep the default 16px or override it only when your design system requires a specific scale.
• Use rem for typography: font-sizes defined in rem scale automatically when the user adjusts browser settings.
• Use rem for spacing: margins, paddings and gaps remain proportional when they share the same root.
• Avoid mixing px and rem without a reason: inconsistent units make scaling harder to predict.
• Use px only for small exceptions: borders, hairline elements or pixel-perfect alignment.
• Avoid setting root font-size in percent to force 10px: the classic 62.5 percent trick adds complexity and can break accessibility expectations.
• Test with browser zoom and custom font-size: this ensures your layout stays readable for all users.

Following these best practices keeps your design predictable, accessible and easier to maintain across breakpoints and devices.

How REM Works in CSS

The rem unit is based on the font-size of the root element, which is the html tag. Unlike em, which depends on the font-size of its parent element, rem always uses a single reference value. This makes it predictable and easy to scale across an entire layout.

For example, if the root font-size is 16px, then:

1rem = 16px

When you define spacing or typography using rem units, the browser calculates the final pixel value by multiplying the rem value by the root font-size. This happens at layout time during the rendering process.

• Root controlled: all rem values use the font-size set on the <code>html</code> element as their reference.
• Respects user settings: if a user increases the browser default font-size for accessibility, all rem-based values scale automatically.
• Not affected by parents: rem stays constant even inside deeply nested components, unlike em.
• Easy global scaling: changing the root font-size adjusts the entire design system without editing multiple components.

In short, rem provides a single source of truth for sizing in CSS, which is why it is used in most modern design systems and UI frameworks.

How To Use REM

Using <code>rem</code> units in your project is straightforward. The main idea is to define a clear root font-size and then use rem consistently for typography, spacing and layout elements. This keeps your entire design scalable and predictable.

1. Set the root font-size

Most projects keep the browser default of 16px. You can set it directly if you want to be explicit:

html {
  font-size: 16px;
}

If your design system uses a different scale, you can adjust it here. Every rem value will be based on this number.

2. Define font sizes using rem

h1 {
  font-size: 2rem;
}

p {
  font-size: 1rem;
}

small {
  font-size: 0.875rem;
}

This makes all text scale together when the root size changes.

3. Use rem for spacing

button {
  padding: 0.75rem 1.25rem;
  margin-top: 1rem;
}

When spacing uses rem, the proportions of your layout stay consistent.

4. Use px only for small fixed values

Borders, 1px lines or sharp UI details are still better in px:

button {
  border: 1px solid #ccc;
}

5. Test with different browser font sizes

Zoom the page or change the browser default font-size. If your layout scales cleanly, you are using rem correctly.

By combining a stable root size with consistent rem usage, you get a layout that is both accessible and easy to maintain across modern devices and screen sizes.

Related Converters:

• REM to PX Converter

  Instantly calculate rem to pixel

• EM to PX Converter

  Instantly calculate em to pixel

• PX to EM Converter

  Instantly calculate pixel to em

• VH to PX Converter

  Instantly calculate vh to pixel

• PX to VW Converter

  Instantly calculate pixel to vw

• PX to Percent Converter

  Instantly calculate pixel to percent