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1004.1.2 • Public • Published

postcss-rem-to-pixel NPM version

A plugin for PostCSS that generates px units from u units.


$ npm install postcss-rem-to-pixel --save-dev


Sometimes you need to include a third-party css file that uses u's. Great pracitice! Unless you can't afford to change your body font-size just for some vendor. This script converts every u value to a px value from the properties you choose using a default font size of 8px.


With the default settings, only font related properties are targeted.

// input
h1 {
    margin: 0 0 20px;
    font-size: 2u;
    line-height: 1.2;
    letter-spacing: 0.0625u;
// output
h1 {
    margin: 0 0 20px;
    font-size: 16px;
    line-height: 1.2;
    letter-spacing: 0.5px;


var fs = require('fs');
var postcss = require('postcss');
var remToPx = require('postcss-rem-to-pixel');
var css = fs.readFileSync('main.css', 'utf8');
var options = {
    replace: false
var processedCss = postcss(remToPx(options)).process(css).css;
fs.writeFile('main-px.css', processedCss, function (err) {
  if (err) {
    throw err;
  console.log('Rem file written.');


Type: Object | Null

    rootValue: 8,
    unitPrecision: 5,
    propList: ['*'],
    selectorBlackList: [],
    replace: true,
    mediaQuery: false,
    minUnitValue: 0
  • rootValue (Number) The root element font size.
  • unitPrecision (Number) The decimal precision px units are allowed to use, floored (rounding down on half).
  • propList (Array) The properties that can change from u to px.
    • Values need to be exact matches.
    • Use wildcard * to enable all properties. Example: ['*']
    • Use * at the start or end of a word. (['*position*'] will match background-position-y)
    • Use ! to not match a property. Example: ['*', '!letter-spacing']
    • Combine the "not" prefix with the other prefixes. Example: ['*', '!font*']
  • selectorBlackList (Array) The selectors to ignore and leave as u.
    • If value is string, it checks to see if selector contains the string.
      • ['body'] will match .body-class
    • If value is regexp, it checks to see if the selector matches the regexp.
      • [/^body$/] will match body but not .body
  • replace (Boolean) replaces rules containing u's instead of adding fallbacks.
  • mediaQuery (Boolean) Allow u to be converted in media queries.
  • minUnitValue (Number) Set the minimum u value to replace.

Use with gulp-postcss and autoprefixer

var gulp = require('gulp');
var postcss = require('gulp-postcss');
var autoprefixer = require('autoprefixer');
var remToPx = require('postcss-rem-to-pixel');
gulp.task('css', function () {
    var processors = [
            browsers: 'last 1 version'
            replace: false
    return gulp.src(['build/css/**/*.css'])

A message about ignoring properties

// `u` is converted to `px`
.convert {
    font-size: 1u; // converted to 16px
// `U`is ignored by `postcss-rem-to-pixel`
.ignore {
    border-width: 2U; // ignored


npm i @startupjs/postcss-rem-to-pixel

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