The article proposes an alternative methodology for the comparison of Gross Domestic Products (GPDs). It is an alternative to the purchasing power parity theory that utilizes the nominal exchange rate to compare GPDs. The value of the money in the conception of Hilferding is obtained dividing the GPDs by the necessary working hours for producing it. The productive power of a society is represented by the value of the money of each society and the relative productive power is represented by the relationship between the values of money (VMb/VMa) that gives the relevant exchange rate to compare the two economies (the dimension of the division of the two money values is the same dimension of the nominal exchange rate, in other words, real for dollar).