下面的例子说明了这个原则：如果一瓶美国葡萄酒可以20美元的价格出售，名义汇率是每美元0.8欧元，那么这瓶美国葡萄酒价值20 x 0.8 = 16欧元。如果一瓶欧洲葡萄酒的价格为15欧元，则16欧元可以购买16/15 = 1.07瓶欧洲葡萄酒。把所有的碎片放在一起，这瓶美国葡萄酒可换成1.07瓶欧洲葡萄酒，实际汇率是每瓶美国葡萄酒1.07瓶欧洲葡萄酒。互惠关系与实际汇率一样，与名义汇率相同。在这个例子中，如果实际汇率是每瓶美国葡萄酒1.07瓶欧洲葡萄酒，那么实际汇率也是每瓶欧洲葡萄酒的1 / 1.07 = 0.93瓶美国葡萄酒。在数学上，实际汇率等于名义汇率乘以项目的国内价格除以项目的国外价格。在单位工作时，很明显这种计算结果是每单位国内商品的外国商品单位。实际上，实际汇率通常是针对一个经济体中的所有商品和服务而不是针对单一商品或服务计算的。这可以简单地通过使用国内和国外的总价格（例如消费者价格指数或GDP平减指数）来代替特定商品或服务的价格来实现。使用这一原则，实际汇率等于名义汇率乘以国内总价格水平除以外国总价格水平。直觉可能表明实际汇率应该等于1，因为并不是很明显为什么给定数量的货币资源无法在不同国家购买相同数量的东西。事实上，实际汇率等于1的这一原则被称为购买力平价，并且存在购买力平价在实践中不需要保持的各种原因。
The following example illustrates this principle: If a bottle of American wine can be sold for $20 and the nominal exchange rate is 0.8 Euro per dollar, then the value of this bottle of American wine is 20 x 0.8 = 16 euros. If the price of a bottle of European wine is 15 euros, then 16 euros can buy 16/15 = 1.07 bottles of European wine. Putting all the pieces together, this bottle of American wine can be exchanged for 1.07 bottles of European wine, the actual exchange rate is 1.07 bottles of European wine per bottle of American wine. The reciprocal relationship is the same as the real exchange rate and the same as the nominal exchange rate. In this example, if the actual exchange rate is 1.07 bottles of European wine per bottle of US wine, the actual exchange rate is also 1 / 1.07 = 0.93 bottles of American wine per bottle of European wine. Mathematically, the actual exchange rate is equal to the nominal exchange rate multiplied by the domestic price of the item divided by the foreign price of the item. When working in a unit, it is clear that this calculation is a foreign commodity unit per unit of domestic commodity. In fact, the real exchange rate is usually calculated for all goods and services in an economy rather than for a single good or service. This can be achieved simply by using domestic and foreign total prices (such as consumer price indices or GDP deflator) instead of the price of a particular good or service. Using this principle, the actual exchange rate is equal to the nominal exchange rate multiplied by the total domestic price level divided by the foreign total price level. Intuition may indicate that the real exchange rate should equal 1 because it is not obvious why a given number of monetary resources cannot purchase the same amount of money in different countries. In fact, the principle that the real exchange rate is equal to 1 is called purchasing power parity, and there are various reasons why purchasing power parity does not need to be maintained in practice.