ECB Exchange

Gem Version Travis Build Status Maintainability Test Coverage Gem Dependency Status

Currency conversion using the European Central Bank's foreign exchange rates. Rates for the last 90 days are fetched and cached on demand. All calculations are performed and returned as BigDecimal, usually a good idea when dealing with money.


  • Ruby >= 2.1.0


Add this line to your Gemfile and run bundle install:

gem 'ecb_exchange'


To convert an amount from one currency to another use:

ECB::Exchange.convert(100, from: 'EUR', to: 'GBP')
=> 0.88235e2

The converted amount (using today's current rate) will be returned (as a BigDecimal). In doing so the gem will have fetched and cached ECB rates for the last 90 days.

You can ask the exchange to convert an amount on a specific date:

ECB::Exchange.convert(100, from: 'EUR', to: 'GBP', date: Date.parse('2017-01-11'))
=> 0.87235e2

To return only the exchange rate multiplier between two currencies use:

ECB::Exchange.rate(from: 'EUR', to: 'USD')
=> 0.11969e1
# you can pass an optional `date` argument to this method too

You can ask for an array of supported currency codes with:

=> ["USD", "JPY", "BGN", "CZK", "DKK", "GBP", "HUF" ... ]

Finally, you can adjust the rates endpoint by setting the XMLFeed.endpoint (e.g. in an initializer):

ECB::Exchange::XMLFeed.endpoint = ""

The XML feed must conform to the ECB rates structure.

Handling Errors

Not all dates, rates or currencies may be available, or the remote endpoint could be unresponsive. You should consider handling the following errors:

  • ECB::Exchange::DateNotFoundError
  • ECB::Exchange::CurrencyNotFoundError
  • ECB::Exchange::ResponseError
  • ECB::Exchange::ParseError

Or rescue ECB::Exchange::Error to catch any of them.


By default rates will be cached to one of the following backend stores (with this order of preference).

  • Your own backend cache store (see below)
  • The Rails.cache
  • An ECB::Exchange::MemoryCache instance (a simple in memory cache store)

To configure your own backend store:

ECB::Exchange::Cache.backend =
# your cache must implement public `read(key)` and `write(key, value)` methods

All keys in the cache are name-spaced with a ecb_exchange_rates_for_date- prefix.


Check out this repo and run bin/setup, this will install gem dependencies and generate docs. Use bundle exec rake to run tests and generate a coverage report.

You can also run bin/console for an interactive prompt allowing you to experiment with the code.


MiniTest is used for testing. Run the test suite with:

$ rake test


Generate docs for this gem with:

$ rake rdoc


If you think something is broken or missing, please raise a new issue. Please remember to check it hasn't already been raised.


Bug reports and pull requests are welcome on GitHub. When submitting pull requests, remember to add tests covering any new behaviour, and ensure all tests are passing on Travis. Read the contributing guidelines for more details.

This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct. See here for more details.


  • Better rdoc documentation
  • A small Rails app to demo this gem, with a one-click heroku install
  • Allow Net::HTTP to be swapped out for any another HTTP client


The code is available as open source under the terms of LGPL-3.