CSS Unit Converter

Convert between px, rem, em, pt, vh, vw, cm, mm, in and %

rem

1

em

1

pt

12.0003

vh

1.111111

vw

1.111111

cm

0.423333

mm

4.233331

in

0.166667

%

100

About the CSS Unit Converter

This CSS unit converter moves between px, rem, em, vh, vw and percentages, with a configurable root font size and viewport dimensions so the relative units resolve against the values your project actually uses.

A CSS unit converter is needed because relative units only mean something in context. A rem is relative to the root font size, an em to the element's own font size, and vh and vw to the viewport — so 1.5rem is 24px only if the root is 16px.

That context is what the converter asks for. Change the root font size and every rem value shifts, which is exactly what happens on a site that sets html font-size to 62.5% so 1rem equals 10px.

Relative units are worth preferring for anything type-related, because they scale when a reader increases their browser font size while px does not. That is an accessibility difference rather than a stylistic preference — a px-based layout simply ignores the setting.

How to use the CSS Unit Converter

  1. Set the root font size. Enter the html font size your project uses, usually 16px.
  2. Enter your value. Type the measurement to convert.
  3. Choose the units. Pick what you have and what you want.
  4. Copy the result. Take the converted value into your stylesheet.

CSS Unit Converter features

  • Multiple CSS units support
  • PX REM EM PT conversion
  • Viewport units (VH VW)
  • Print units (CM MM IN)
  • Responsive design calculations
  • Base font size configuration
  • Parent element sizing
  • Real-time conversion
  • Professional accuracy
  • Web development focused

Frequently asked questions

What CSS units are supported for conversion?

Comprehensive support for: px (pixels), rem (root em), em (relative em), pt (points), vh (viewport height), vw (viewport width), cm (centimeters), mm (millimeters), in (inches), and % (percentage) for complete CSS unit conversion.

How do CSS unit conversions work?

Uses precise conversion algorithms: 1in = 96px, 1cm = 37.7953px, 1mm = 3.77953px, 1pt = 1.3333px. Relative units (rem, em, %) use base font size and parent element values for accurate responsive design calculations.

When should I use different CSS units?

Use px for precise control, rem for scalable typography, em for relative sizing, vh/vw for viewport-based responsive design, cm/mm/in for print media, and % for flexible layouts. Each unit serves specific design requirements.

What are the benefits of using rem and em units?

Rem units scale with root font size for consistent typography and accessibility. Em units scale with parent font size for component-relative sizing. Both support responsive design and improve user experience across devices.

How do viewport units (vh, vw) work?

Viewport units are relative to browser viewport dimensions: 1vh = 1% of viewport height, 1vw = 1% of viewport width. Essential for responsive design, full-screen layouts, and device-specific sizing without media queries.

Can this converter handle responsive design calculations?

Yes! Supports responsive design calculations with base font size, viewport dimensions, and parent element values. Perfect for converting between absolute and relative units for responsive web development.

Is this suitable for professional web development?

Absolutely! Essential for web developers, UI/UX designers, and front-end engineers. Perfect for responsive design, CSS optimization, accessibility compliance, and modern web development workflows.