Web Tools

CSS Unit Converter

Convert values between pixels, rem and em with a configurable base font size.

CSS value

From To Base font size (px)

Converted value

What this tool does

Relative CSS units make interfaces easier to scale, but conversions depend on a base font size. This tool shows the calculation and the final value.

How to use it well

Start with a small sample, check the output, then paste the full text when the result looks right. For important production data, review the output before saving or sharing it.

Common uses

Convert design measurements
Move from px to rem
Check typography and spacing values

CSS Unit Converter workflow

Use this css unit converter when you need a fast browser-based check before moving data into code, documentation, a report or another web tool. Start with a small sample, confirm the result, then process the full pasted text so mistakes are easier to catch.

Why it helps

The goal is to keep the task focused: paste input, run the conversion or check, then review a clear output without installing software. This is useful for developers, content teams, SEO work, support notes and quick QA checks.

Related FormatKit tools

Color Converter HEX RGB HSL , CSS Minifier & Compressor , JavaScript Minifier can help when the next step is formatting, converting or cleaning the same data.

Guide

PX, REM and EM: Choosing CSS Units That Scale

Understand the difference between fixed and relative CSS units before converting design values.

Read guide

Questions

What base size should I use?

Browsers commonly use 16px, but your root or parent font size may be different. Enter the value used by your project.

Are rem and em always identical?

No. Rem uses the root font size, while em uses the current element context. This calculator uses the entered base for either relative unit.