The exchange rate of a currency against the U.S. dollar (USD). Most currencies that are traded in international markets are quoted in terms of number of units of foreign currency per USD. However, some currencies, such as the euro, British pound and Australian dollar, are quoted in terms of U.S. dollars per foreign currency. 




|||Since practically all currencies use the USD as the base currency, it is easy to calculate cross currency rates - which are exchange rates for one currency in terms of another currency that is not the US dollar. However, particular care must be taken when calculating such rates, especially if the currencies involved include those that are quoted in terms of USD per foreign currency.