Network Tools

CSS Unit Converter

Convert CSS units

Convert values between CSS units (px, rem, em, %) with customizable base font sizes. Main function - unit conversion table, additional - CSS code conversion with nesting support.

16px(16px)

Conversion Table

px
16.0000
rem
1.0000
em
1.0000
%
100.0000

Preset Values Table

Commonly used values, automatically converted based on base font size

pxremem%
4px
0.2500rem
0.2500em
25.0000%
6px
0.3750rem
0.3750em
37.5000%
8px
0.5000rem
0.5000em
50.0000%
10px
0.6250rem
0.6250em
62.5000%
12px
0.7500rem
0.7500em
75.0000%
14px
0.8750rem
0.8750em
87.5000%
16px
1.0000rem
1.0000em
100.0000%
18px
1.1250rem
1.1250em
112.5000%
20px
1.2500rem
1.2500em
125.0000%
24px
1.5000rem
1.5000em
150.0000%
28px
1.7500rem
1.7500em
175.0000%
32px
2.0000rem
2.0000em
200.0000%
36px
2.2500rem
2.2500em
225.0000%
40px
2.5000rem
2.5000em
250.0000%
48px
3.0000rem
3.0000em
300.0000%
56px
3.5000rem
3.5000em
350.0000%
64px
4.0000rem
4.0000em
400.0000%
72px
4.5000rem
4.5000em
450.0000%
80px
5.0000rem
5.0000em
500.0000%
96px
6.0000rem
6.0000em
600.0000%

Online CSS Unit Converter: px, rem, em and % — Complete Guide

In modern web development, adaptability and accessibility of interfaces play a crucial role. Our CSS Unit Converter is a powerful tool for frontend developers and web designers that automates font size and spacing calculations. Forget about calculators and manual formulas: convert px to rem, em, or percentages instantly.

How does the CSS converter work?

The tool works in two modes, covering all layout needs: from converting a single value to processing entire code fragments.

Base Font Size

All relative units (rem, em, %) depend on the base font size. By default in browsers this is 16px, but design systems often use 14px, 18px, or 20px. Our tool allows you to set any base size and saves it in tab settings. You can create separate tabs for different projects and switch between them without losing context.

Instant Conversion (Unit Converter)

Simply enter a value in any field (e.g., in pixels), and the calculator will automatically recalculate it to other units:

  • PX (Pixels): Absolute unit, precise and predictable.
  • REM (Root EM): Relative to the root <html> element. The standard for adaptive typography.
  • EM: Relative to the parent element. Perfect for scalable components.
  • % (Percentage): Percentage ratio of the base size.

CSS Code Conversion with Nesting Support

A unique feature of our service is the CSS Code Converter mode. Paste your CSS code, select the conversion direction (e.g., from px to rem), and the algorithm will process the entire code. The tool accounts for selector nesting and parent font-size properties to correctly calculate complex em values.

PX vs REM vs EM: What to Choose?

Understanding the difference between units is critically important for quality layout.

Why Use REM Instead of PX?

Using rem allows users to scale the interface through browser settings (e.g., for visually impaired users). If a site is hardcoded in px, changing the font size in the browser won't affect the layout, which degrades accessibility (a11y).

When to Use EM?

The em unit is useful for creating components where spacing (padding, margin) should depend on the element's own font size. However, you need to be careful with em due to the compounding effect. Our converter helps track these dependencies.

Advantages of Our Tool

  • Multitasking: The tab system allows you to work on multiple projects simultaneously, preserving settings for each.
  • Progress Saving: All data, including the active tab and rounding settings, is automatically saved in the browser's LocalStorage. You won't lose data when reloading the page.
  • Flexible Settings: Choose rounding precision (number of decimal places) so your code meets your team's standards.

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Intro

A CSS unit converter helps you convert style values between CSS units such as px, rem, em, %, vw, vh, and sometimes pt. This is useful in responsive design, typography, spacing systems, and component libraries where the same visual size may need different units depending on context.

For example, a designer may hand off a margin in pixels, but your front-end system may prefer rem for accessibility and scalability. A font size that looks fine in px may need to become em inside a component, or a layout width may work better in viewport units. Instead of estimating values manually, the converter gives you faster and more consistent results.

This tool is helpful when refactoring old CSS, moving from fixed to responsive layouts, or building design tokens. It can also improve collaboration between designers and developers because everyone can compare the same values in the units they actually use.

How to Use

1. Enter the numeric value and choose the source unit, such as px or rem. 2. Set the base value if needed, for example the root font size for rem calculations. 3. View the converted result and copy the unit you need for your stylesheet.

Examples

  • Input: 16px with base 16px

Output: 1rem

  • Input: 24px with base 16px

Output: 1.5rem

  • Input: 50vw on a 1200px-wide viewport

Output: 600px

Tips

  • Confirm the base font size before converting between px, rem, and em.
  • Prefer rem for scalable typography in many modern interfaces.
  • Use viewport units carefully on mobile because visible screen height can change.

FAQ

What is the difference between rem and em?

rem is based on the root font size, while em depends on the current element’s font size.

Why convert px to rem?

Because rem often scales better for accessibility, zoom, and consistent design systems.

Are viewport units always reliable?

They are useful, but mobile browsers can make vh behave differently as browser chrome appears or disappears.