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Convert px to rem in css files with optional fallback to px.

Getting Started

This plugin requires Grunt ~0.4.2

If you haven't used Grunt before, be sure to check out the Getting Started guide, as it explains how to create a Gruntfile as well as install and use Grunt plugins. Once you're familiar with that process, you may install this plugin with this command:

npm install grunt-px-to-rem --save-dev

Once the plugin has been installed, it may be enabled inside your Gruntfile with this line of JavaScript:


The "px_to_rem" task



Type: Int Default value: 16

Base size


Type: Boolean Default value: false

Keep initial px values for fallback to browser who doesn't support rem.


Type: Boolean Default value: false

Create px fallback for existing rem units. (options.fallback needs to be true)


Type: Array Default value: []

Array of properties that px-to-rem should ignore. Ex: ['border-left','border-top']

Type: Boolean|Object Default value: false

If the map option isn't defined or is set to false, px_to_rem will neither create nor update a sourcemap.

If true is specified, px_to_rem will try to find a sourcemap from a previous compilation step using an annotation comment (e.g. from Sass) and create a new sourcemap based on the found one (or just create a new inlined sourcemap). The created sourcemap can be either a separate file or an inlined map depending on what the previous sourcemap was.

You can gain more control over sourcemap generation by setting an object to the map option:

  • prev (string or false): a path to a directory where a previous sourcemap is (e.g. path/). By default, px_to_rem will try to find a previous sourcemap using a path from the annotation comment (or using the annotation comment itself if the map is inlined). You can also set this option to false to delete the previous sourcemap.
  • inline (boolean): whether a sourcemap will be inlined or not. By default, it will be the same as a previous sourcemap or inlined.
  • annotation (boolean or string): set this option to true or false to enable or disable annotation comments. You can also overwrite an output sourcemap path using this option, e.g. path/ (by default, px_to_rem will save your sourcemap to a directory where you save CSS). This option requires inline to be false or undefined.
  • sourcesContent (boolean): whether original contents (e.g. Sass sources) will be included to a sourcemap. By default, px_to_rem will add contents only for new sourcemaps or if a previous sourcemap has them.


Type: Int Default value: 20

Set max decimals on rem values.

Usage Examples

Default Options

  px_to_rem: {
    dist: {
      options: {
        base: 16,
        fallback: false,
        fallback_existing_rem: false,
        ignore: [],
        map: false
      files: {
        'dest/style.css': ['src/style.css']

CSS usage

div {
  font-size: 16px; // Converts to rem
  border-left: 1pxi solid #000000; // Returns 1px (pxi = px important)