Convert between pixels, rem, em, and viewport units
System Definition BlockConvert between pixels, rem, em, and viewport units instantly. Essential for building accessible, fluid, and responsive web interfaces based on modern CSS standards.
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The calculator uses a dynamic math engine based on the browser's Root Font Size. By default, most browsers set the root `<html>` font size to 16px. When you input a pixel value (e.g., 24px), the tool divides it by the base font size (24 / 16) to generate the equivalent REM value (1.5rem). The base font size can be globally adjusted to match your specific CSS reset rules.
:root {
/* Base font size (1rem = 16px) */
font-size: 100%;
}
.container {
/* Scales correctly on mobile and desktop */
max-width: 75rem;
padding: 2rem;
margin-inline: auto;
}Pixels are absolute units. If a visually impaired user increases their browser's default font size (from 16px to 24px) to read better, any text hard-coded in PX will ignore their settings and remain small. REM units scale proportionally with the user's preference, ensuring your site remains accessible.
REM stands for 'Root EM' and is always relative to the root `<html>` font size. EM is relative to the font size of its *direct parent element*. EM can cause compounding sizing issues if nested deeply (e.g., an EM inside an EM), making REM the safer and more predictable choice for global layouts.
Viewport Width (VW) and Viewport Height (VH) are relative to the size of the browser window itself. 1vw is exactly 1% of the screen's width. These units are incredibly powerful for creating full-screen hero sections or fonts that grow seamlessly as the browser stretches.
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