A purchasing power parity (PPP) is defined as the number of units of B’s currency that are needed in B to purchase the same quantity of individual good or service as one unit of A’s currency will purchase in A.

Typically, a PPP for a country is expressed in terms of the currency of a base country, with the US dollar commonly being used. PPPs are thus weighted averages of the relative prices, quoted in national currency, of comparable items between countries. Used as deflators, they enable cross-country comparisons of GDP and its expenditure components.

Система национальных счетов 2008