Responsive, readable typography is one of the smallest details that makes a site feel polished. This short guide explains how and why designers and Next.js developers prefer relative units — rem and em — over absolute pixels, and gives practical patterns you can apply without building or exposing a converter tool. Throughout the article you’ll see the keywords people search for: px to rem, px to em, converter px to rem, and related phrases — useful for SEO if you want to attract developers and designers.
Accessibility & scalability. rem and em scale with user preferences and browser settings. That makes text more accessible to users who need larger type.
Predictable hierarchy. rem is relative to the root (<html>) font-size and is great for consistent global sizing. em is relative to the parent element and is useful for component-scoped scaling (buttons, cards, modulable components).
Consistency across devices. Using relative units helps maintain visual rhythm across breakpoints without rewriting many pixel values.
Searchers often look for px to rem or px to em guidance when converting a static design into a responsive page — these queries signal intent to implement accessible typography.
Set a root size with accessibility in mind
Keep the browser default (16px) or set a sensible root font-size in CSS. Using html { font-size: 100%; } or html { font-size: 16px; } is a common starting point. That way a designer familiar with pixel values can reason about conversions (see note below).
Prefer rem for global scale, em for local scale
Use rem for headings, paragraphs, and layout spacing that should scale uniformly. Use em inside components where size should respect the component’s context (for example, an icon inside a button that should grow with the button text).
Use CSS custom properties for a consistent scale
Define a typographic scale using CSS variables (--step-0, --step-1, etc.). This makes it easy to tweak values in one place and keeps components DRY.
Leverage clamp() and fluid typography
Modern CSS clamp() lets you create fluid sizes that adapt to viewport width while remaining bounded — great for hero headings. This is a layout technique rather than a conversion tool, but it pairs nicely with rem values for predictable scaling.
Document the base assumptions in your design system
Explicitly record the root font-size and the intended mapping between design pixels and rem or em. That helps new team members and keeps SEO-focused copy (like “px to rem” articles or docs) consistent.
Need a converter right now? Try this online px → rem converter: px to rem converter by AlterDraft.
rem is relative to the root (<html>) font-size and is ideal for global typographic scale.
em is relative to the parent element’s font-size and is useful for component-level scaling.
For fast and accurate conversion, you can use the link to a special tool: https://alterdraft.com/px-to-rem
