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CSS Unit Converter

Convert between CSS units - px, rem, em, vw, vh, pt, and percent. Configure root font size, parent font size, and viewport dimensions.

How to Use

  1. Step 1: Enter a value and select its unit (e.g. 16px).
  2. Step 2: Set the base font size, parent font size, and viewport dimensions if needed.
  3. Step 3: All converted values appear instantly. Click any result to use it as the new input.

Frequently Asked Questions

What is the difference between rem and em?

rem is relative to the root element font size (usually 16px on most browsers). em is relative to the current element's parent font size, which can compound/cascade.

When should I use rem vs px?

Use rem for font sizes and spacing so your layout scales with user's browser font settings (better accessibility). Use px for fine-grained control, borders, or fixed elements.

When should I use px vs rem vs em?

px: fixed-size elements (borders, shadows, icons); rem: font sizes and spacing — scales with root font size for better accessibility; em: sizes relative to parent element; vw/vh: full-screen layouts and responsive design. Using rem for text ensures your layout respects user browser font size preferences.

When should I use rem instead of px?

rem is relative to the root font size, enabling responsive typography — when a user adjusts font size in browser settings, rem-based elements scale proportionally, improving accessibility. px is best for fixed dimensions (e.g., 1px borders). Best practices: use rem for font sizes, spacing, and container widths; use px for borders and shadows; use em in media queries.