What is the default root font size?

Most browsers set the root font size to 16px by default. If you change it in your CSS (e.g. html { font-size: 18px; }), update the root size field to match.

How do I convert rem to px?

Multiply the rem value by the root font size in pixels. For example, 1.5rem × 16px = 24px.

How do I convert px to rem?

Divide the pixel value by the root font size. For example, 24px ÷ 16px = 1.5rem.

Why use rem instead of px?

rem units scale relative to the document root font size, making layouts accessible when users change their browser font size preference. px is absolute and does not scale.

Does this tool work for em units too?

The math is the same for em when the element's own font size equals the root font size. For nested elements where em is relative to the parent, you would need to enter the parent font size as the root size.

Rem To Px Converter

Name: Rem To Px Converter
Availability: InStock
Author: Nham Vu

Convert CSS rem values to pixels (and px to rem) instantly with a configurable root font size.

Root Font Size (px)

Set to match your CSS html { font-size: ... } value.

rem → px

rem

— px

px → rem

— rem

Reference Table

Root: 16px

rem	px	Common use

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Summary

Convert CSS rem values to pixels (and px to rem) instantly with a configurable root font size.

How it works

Set the root font size (default 16px, matching browser defaults).
Enter a rem value to convert it to pixels, or enter a px value to get rem.
The result updates instantly as you type.
Use the bulk table to see common rem values and their pixel equivalents at a glance.
Copy any result to the clipboard with one click.

Use cases

Convert design mockup pixel sizes to rem for scalable CSS layouts.
Check what a rem value renders to in pixels at a given root font size.
Verify that spacing and typography values are consistent across breakpoints.
Quickly generate a reference table for a design system.
Translate px values from a design file into responsive rem units.

Frequently Asked Questions

Last updated: 2026-06-09 · Reviewed by Nham Vu