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    5.1.1 • Public • Published

    postcss-pxtoremorem NPM version

    A plugin for PostCSS that generates rem or em units from pixel units.


    $ npm install postcss-pxtoremorem --save-dev


    Pixels are the easiest unit to use (opinion). The only issue with them is that they don't let browsers change the default font size of 16. This script converts every px value to a rem or em from the properties you choose to allow the browser to set the font size.


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

    // input
    h1 {
        margin: 0 0 20px;
        font-size: 32px;
        line-height: 1.2;
        letter-spacing: 1Px;
    // output
    h1 {
        margin: 0 0 20px;
        font-size: 2rem;
        line-height: 1.2;
        letter-spacing: 0.0625em;


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


    Type: Object | Null

        rootValue: 16,
        unitPrecision: 5,
        propList: ['font', 'font-size', 'line-height', 'letter-spacing'],
        selectorBlackList: [],
        replace: true,
        mediaQuery: false,
        minPixelValue: 0,
        exclude: /node_modules/i
    • rootValue (Number | Function) Represents the root element font size or returns the root element font size based on the input parameter
    • unitPrecision (Number) The decimal numbers to allow the REM or EM units to grow to.
    • propList (Array) The properties that can change from px to rem or em.
      • 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 px.
      • 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 rems or ems instead of adding fallbacks.
    • mediaQuery (Boolean) Allow px to be converted in media queries.
    • minPixelValue (Number) Set the minimum pixel value to replace.
    • exclude (String, Regexp, Function) The file path to ignore and leave as px.
      • If value is string, it checks to see if file path contains the string.
        • 'exclude' will match \project\postcss-pxtoremorem\exclude\path
      • If value is regexp, it checks to see if file path matches the regexp.
        • /exclude/i will match \project\postcss-pxtoremorem\exclude\path
      • If value is function, you can use exclude function to return a true and the file will be ignored.
        • the callback will pass the file path as a parameter, it should returns a Boolean result.
        • function (file) { return file.indexOf('exclude') !== -1; }

    Use with gulp-postcss and autoprefixer

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

    A message about ignoring properties

    Currently, the easiest way to have a single property ignored is to use a capital in the pixel unit declaration.

    // `px` is converted to `rem`
    .convert {
        font-size: 16px; // converted to 1rem
    // `Px` is converted to `em`
    .convert {
        font-size: 16Px; // converted to 1em
    // `PX` is ignored by `postcss-pxtoremorem` but still accepted by browsers
    .ignore {
        border: 1PX solid; // ignored
        border-width: 2PX; // ignored


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