active-shipping-example.rb

include ActiveMerchant::Shipping
usps = USPS.new(:login => '123JAMES4567')

origin = Location.new(:country => 'US', :zip => '90210')
destination = Location.new(:country => 'CA', :postal_code => 'K2P 0K3')

grams = 100
centimetres = [20,10,10]
packages = [Package.new(grams, centimetres)]

response = usps.find_rates(origin, destination, packages)
rates = response.rates.sort_by(&:price)
cheapest = rates.map {|r| [ r.service_name,
                            r.price.to_f / 100, # rates returned in cents
                            r.currency]}.first
# => ["USPS First-Class Mail International", 1.62, "USD"]