Evaluates plural rules, so that localization libraries can choose the right plural form.

Usage no npm install needed!

<script type="module">
  import pluralRules from '';


Plural Rules

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Evaluates locale-specific plural rules to identify the right plural form for a cardinal number, which represents an item count. Internationalization libraries can utilize it to choose the right localized string.

  • Tiny code base - 2.52 kB, 1.57 KB minified, 0.67 KB gzipped. Do not pack unnecessary weight in your application. (Bundled code for the web browser is 11 kB, 4.77 kB minified, 1.79 kB gzipped.)
  • Packed data - 18.2 kB, 16 kB minified, 3 kB gzipped. A quarter of the size of the original CLDR data. (This size adds to the code size.)
  • Generated from the official CLDR plural rules version 35.1. Cardinals for almost 200 languages are supported.
  • Minimal interface for finding out the right plural form by evaluating plural rules for a specific locale. Looking up and formatting localizable strings is a task for internationalization libraries.

If you are looking for a smaller and faster library using Mozilla plural rules, see fast-plural-rules.

Table of Contents


const { getPluralFormForCardinal } = require('plural-rules')

// Returns index of the plural form for the specified locale and cardinal.
getPluralFormForCardinal('en', 1) // Returns "one";   "1 file"
getPluralFormForCardinal('en', 2) // Returns "other"; "2 files"
getPluralFormForCardinal('en', 5) // Returns "other"; "5 files"
getPluralFormForCardinal('cs', 1) // Returns "one";   "1 soubor"
getPluralFormForCardinal('cs', 2) // Returns "few";   "2 soubory"
getPluralFormForCardinal('cs', 5) // Returns "other"; "5 souborů"

// Returns a localized message for the specified locale and cardinal.
localizeMessage('en', 'fileCount', 3) // Returns "3 files"
localizeMessage('cs', 'fileCount', 3) // Returns "3 soubory"

// Returns a localized message for the specified locale and cardinal.
function localizeMessage (locale, messageKey, cardinal) {
  const pluralForm = getPluralFormForCardinal(locale, cardinal)
  const messageFormat = messages[locale][messageKey][pluralForm]
  return messageFormat.replace('{0}', cardinal)
// Localized messages organized by locales and message keys.
const messages = {
  en: {
    fileCount: {
      one:   '{0} file', // singular
      other: '{0} files' // plural
  cs: {
    fileCount: {
      one:   '{0} soubor',  // singular
      few:   '{0} soubory', // plural for 2-4 items
      other: '{0} souborů'  // plural for 5 and more items

Installation and Getting Started

This module can be installed in your project using NPM or Yarn. Make sure, that you use Node.js version 6 or newer.

$ npm i plural-rules --save
$ yarn add plural-rules

Functions are exposed as named exports, for example:

const { getPluralFormForCardinal } = require('plural-rules')

You can read more about the module loading in other environments, like with ES6 or in web browsers. Usage scenarios demonstrate applications of this library in typical real-world situations. Design concepts explain the approach to the correct internationalization of messages with cardinals taken by this library. Translators will read about plural rules for supported languages to be able to write the right plural forms to language packs. Data genrator enables customizing the the amount of recognized languages and thus shrink the library size. Finally, the API reference lists all functions with a description of their functionality.


In lieu of a formal styleguide, take care to maintain the existing coding style. Add unit tests for any new or changed functionality. Lint and test your code using Grunt.

Release History

  • 2019-08-03 v1.0.0 Decrease the size of the packed plural rules and forms
  • 2019-08-03 v0.1.0 Upgrade CLDR data to the version 35.1
  • 2018-11-05 v0.0.1 Initial release


Copyright (c) 2018-2019 Ferdinand Prantl

Licensed under the MIT license.