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A Ruby Library for dealing with money and currency conversion.

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This library aids one in handling money and different currencies. Features:

  • Provides a Money class which encapsulates all information about an certain amount of money, such as its value and its currency.

  • Provies a Money::Currency class which encapsulates all information about a monerary unit.

  • Represents monetary values as integers, in cents. This avoids floating point rounding errors.

  • Represents currency as Money::Currency instances providing an high level of flexibility.

  • Provides APIs for exchanging money from one currency to another.

  • Has the ability to parse a money and currency strings into the corresponding Money/Currency object.



Starting in v3.1.0 we will be making two changes to the exchange process. First a new `Bank::Base` class will be available. This will allow users to more easily create custom `Bank` classes. Secondly the default `#exchange` method will be depreciated and a new `#exchange_with` method will be used. Currently `#exchange` passes the `cents` attribute. `#exchange_with` will pass the actual `Money` object instead.


Install stable releases with the following command:

gem install money

The development version (hosted on Github) can be installed with:

git clone git://
cd money
rake install



require 'money'

# 10.00 USD
money =, "USD")
money.cents     # => 1000
money.currency  # =>"USD"), "USD") ==, "USD")   # => true, "USD") ==, "USD")    # => false, "USD") ==, "EUR")   # => false


Currencies are consistently represented as instances of Money::Currency. The most part of Money APIs allows you to supply either a String or a Money::Currency., "USD") ==,"USD")), "EUR").currency =="EUR")

A Money::Currency instance holds all the information about the currency, including the currency symbol, name and much more.

currency =, "USD")
# => "USD"
# => "United States Dollar"

To define a new Money::Currency simply add a new item to the Money::Currency::TABLE hash, where the key is the identifier for the currency object and the value is a hash containing all the currency attributes.

Money::Currency::TABLE[:usd] = {
  :priority => 1,
  :iso_code => "USD",
  :name     => "United States Dollar",
  :symbol   => "$",
  :subunit  => "Cent"
  :subunit_to_unit => 100,
  :separator => ".",
  :delimiter => ","

The pre-defined set of attributes includes:

* priority: a numerical value you can use to sort/group the currency list
* iso_code: the international 3-letter code as defined by the ISO 4217 standard
* name: the currency name
* symbol: the currency symbol (UTF-8 encoded)
* subunit: the name of the fractional monetary unit
* subunit_to_unit: the proportion between the unit and the subunit
* separator: character between the whole and fraction amounts
* delimiter: character between each thousands place

All attributes are optional. Some attributes, such as :symbol, are used by the Money class to print out a representation of the object. Other attributes, such as :name or :priority, exist to provide a basic API you can take advantage of to build your application.


The priority attribute is an arbitrary numerical value you can assign to the Money::Currency and use in sorting/grouping operation.

For instance, let's assume your Rails application needs to a currency selector like the one available at You can create a couple of custom methods to return the list of major_currencies and all_currencies as follows:

# Returns an array of currency id where
# priority < 10
def major_currencies(hash)
  hash.inject([]) do |array, (id, attributes)|
    priority = attributes[:priority]
    if priority && priority < 10
      array[priority] ||= []
      array[priority] << id

# Returns an array of all currency id
def all_currencies(hash)

# => [ :usd, :eur, :bgp, :cad ]

# => [ :aed, :afn, all, ... ]

Default Currency

By default Money defaults to USD as its currency. This can be overwritten using

Money.default_currency ="CAD")

If you use Rails, then environment.rb is a very good place to put this.

Currency Exchange

Exchanging money is performed through an exchange bank object. The default exchange bank object requires one to manually specify the exchange rate. Here's an example of how it works:

Money.add_rate("USD", "CAD", 1.24515)
Money.add_rate("CAD", "USD", 0.803115)

Money.us_dollar(100).exchange_to("CAD")  # =>, "CAD")
Money.ca_dollar(100).exchange_to("USD")  # =>, "USD")

Comparison and arithmetic operations work as expected:, "USD") <=>, "USD")   # => 1; 9.00 USD is smaller, "EUR") +, "EUR") ==, "EUR")

Money.add_rate("USD", "EUR", 0.5), "EUR") +, "USD") ==, "EUR")

There is nothing stopping you from creating bank objects which scrapes for the current rates or just returns rand(2):

Money.default_bank =

Currency Exchange Implementations

The following is a list of Money.gem compatible currency exchange rate implementations.

Ruby on Rails

Use the compose_of helper to let Active Record deal with embedding the money object in your models. The following example requires a cents and a currency field.

class ProductUnit < ActiveRecord::Base
  belongs_to :product
  composed_of :price,
    :class_name => "Money",
    :mapping => [%w(cents cents), %w(currency currency_as_string)],
    :constructor => { |cents, currency| || 0, currency || Money.default_currency) }

    validate :cents_not_zero

    def cents_not_zero
      errors.add("cents", "cannot be zero or less") unless cents > 0

    validates_presence_of :sku, :currency
    validates_uniqueness_of :sku

For Money 2.2.x and previous versions, simply use the following composed_of definition:

composed_of :price,
  :class_name => "Money",
  :mapping => [%w(cents cents), %w(currency currency)],
  :constructor => { |cents, currency| || 0, currency || Money.default_currency) }

For further details read the full discussion at

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