PostCSS Size Clamp

A PostCSS plugin that generates fluid typography using modern CSS clamp() calculations.

This plugin was inspired by the excellent postcss-responsive-type. We initially forked it to add container query support and cqw calculations, but ultimately decided to create a new plugin leveraging modern CSS capabilities and greater performance.

Unlike its predecessor, this plugin:

• Outputs a single line of CSS using clamp() instead of multiple media/container queries
• Pre-calculates values for optimized browser rendering
• Supports container query units (cqw, cqi, cqb)
• Includes a handy line-height shorthand syntax

Installation

npm install postcss-size-clamp --save-dev

Usage

// postcss.config.js
module.exports = {
	plugins: [
		require('postcss-size-clamp')({
			fontRange: [420, 1620], // default viewport/container range
			fontRangeUnit: 'cqw', // default unit (vw, cqw, cqi, cqb)
		}),
		require('postcss-preset-env'),
	],
};

Basic Usage

.title {
	font-size: responsive 16px 32px;
}

Outputs:

.title {
	font-size: clamp(16px, calc(10.4px + 1.33333cqw), 32px);
}

With Line Height Shorthand

.title {
	font-size: responsive 16px 32px / 1.5;
}

Outputs:

.title {
	font-size: responsive 16px 32px;
	line-height: 1.5;
}

Custom Range and Units

.title {
	font-size: responsive 20px 48px;
	font-range: 768px 1920px;
	font-range-unit: vw;
}

Outputs:

.title {
	font-size: clamp(20px, calc(1.33333px + 2.43056vw), 48px);
}

Features

Global Configuration Set default ranges and units in your PostCSS config to maintain consistency across your project:

require('postcss-size-clamp')({
	fontRange: [420, 1620], // min and max viewport/container width
	fontRangeUnit: 'cqw', // viewport or container query unit
});

Supported Units

• vw: Viewport width
• cqw: Container query width
• cqi: Container query inline size
• cqb: Container query block size

Per-Declaration Overrides Override global settings using font-range and font-range-unit properties:

.custom {
	font-size: responsive 16px 32px;
	font-range: 320px 1440px;
	font-range-unit: cqi;
}

Line Height Shorthand Add line-height using the shorthand syntax:

font-size: responsive <min>px <max>px / <line-height>;

Browser Support

While clamp() has excellent browser support, we recommend using this plugin with postcss-preset-env for maximum compatibility. Place this plugin before postcss-preset-env in your PostCSS config to take advantage of its browser compatibility features.

Performance

This plugin pre-calculates numerical values where possible, resulting in optimized CSS output. Instead of multiple media queries or complex calculations, it generates a single, efficient line of CSS that browsers can process quickly.

License

MIT