What's the difference between rem and em?

rem is always relative to the root element's font size; em is relative to the parent element's font size, so it can compound in nested elements.

CSS Unit Converter

Convert a pixel value to rem and em units based on a configurable root font size, useful for responsive CSS work.

Inputs

Results

Try an example

Formula

rem = px / root font size

Aspect Ratio Scaling and CMYK-to-RGB Conversion Explained

How proportional image resizing works, and how CMYK print colors translate to RGB screen colors.

Aspect Ratio Calculator

Calculate the missing dimension to preserve an aspect ratio.

Base64 Encoder / Decoder

Encode text to Base64 or decode Base64 back to text.

URL Encoder / Decoder

Encode text for safe use in a URL, or decode a URL-encoded string.

Number Base Converter

Convert a number between binary, octal, decimal, and hexadecimal.

Unix Timestamp Converter

Convert between Unix timestamps and human-readable dates.

UUID Generator

Generate a random version 4 UUID.