# Purchasing Power Parity Explained > Purchasing power parity adjusts for the fact that money buys more in some countries than others. Here is what PPP means, how the Big Mac Index illustrates it, and why economists use it to compare living standards. *Section: World — By Liam Chen (World Affairs Reporter) — Published October 7, 2024 — 6 min read* Canonical URL: https://dailyjunction.org/world/what-is-purchasing-power-parity Tags: purchasing power parity, economics, exchange rates, GDP, cost of living ## Key takeaways - Purchasing power parity (PPP) compares currencies by what they can actually buy, rather than by market exchange rates. - The core idea is that a basket of identical goods should, in theory, cost the same in different countries once converted to a common currency. - The Big Mac Index is a light-hearted way to test PPP, comparing the price of one burger around the world. - Economists use PPP to compare living standards and the real size of economies more fairly than market exchange rates allow. - PPP is a theoretical benchmark, not a precise rule; trade barriers, non-traded services and taxes mean prices rarely line up exactly. If you have ever travelled somewhere and been struck by how far your money seemed to stretch, you have already grasped the idea behind one of economics' most useful tools. A pound converted at the airport buys a very different amount of lunch in one country than in another. Purchasing power parity is the concept economists use to make sense of that gap, and it underpins many of the comparisons you see between countries. Here is what it means, how it is measured, and why it matters. ## What purchasing power parity is **Purchasing power parity (PPP) is a way of comparing currencies based on what they can actually buy, rather than on the rate at which they trade on financial markets.** The core principle is simple: a basket of identical goods should, in theory, cost the same in two different countries once you convert one currency into the other. Put another way, PPP asks not "how many dollars equal a pound on the markets today?" but "how many dollars do you need in the United States to buy what a pound buys in Britain?" Those are different questions, and they often give different answers. The reason is that **market exchange rates** are driven by trade, investment flows and speculation, which have little to do with the price of a sandwich or a haircut in a particular town. PPP strips that away and focuses on real prices on the ground. This makes it a close cousin of [GDP](/world/what-is-gdp), because economists often adjust GDP figures using PPP to compare the true size of economies. ## The law of one price Underlying PPP is a tidy idea called the **law of one price**. It says that, in a perfect market with no transport costs or trade barriers, an identical good should sell for the same price everywhere once converted to a common currency. The logic is that if a product were much cheaper in one country, traders would buy it there and sell it where it is dearer, profiting from the difference. That activity would push the cheap price up and the expensive price down until they met. In reality this only works neatly for goods that are easy to trade, but it is the intuition that gives PPP its name: prices should reach *parity*. ## The Big Mac Index The most famous illustration of PPP is also the most fun. In 1986 The Economist created the **Big Mac Index**, which compares the price of a McDonald's Big Mac across dozens of countries. The burger is a clever choice because it is broadly similar everywhere, made from comparable ingredients to a standard recipe, and sold in scores of countries. So if a Big Mac costs the equivalent of £4 in Britain but only £2.50 in another country, that hints the second country's currency may be **undervalued** against the pound relative to PPP, or simply that costs there are lower. > The Big Mac Index was never meant as a precise tool. It was designed to make exchange-rate theory more digestible, and it succeeds, turning an abstract idea into something you can taste. Despite its light-hearted origins, the index captures the heart of PPP: comparing one identical, everyday item to test whether currencies buy what they "should". ## Why economists use PPP For serious comparisons, market exchange rates can mislead, and PPP offers a fairer picture in two main areas. 1. **Comparing living standards.** A salary of £20,000 might feel modest in London but comfortable in a country where rent, food and services are far cheaper. Converting incomes at market exchange rates ignores those differences. PPP adjusts for the local cost of living, so a comparison reflects what people can actually afford. 2. **Measuring the real size of economies.** When you convert national output at market exchange rates, economies with low local prices look smaller than they "feel" to the people living in them. Adjusting for PPP often reveals that such economies are larger in real terms. This is why bodies like the International Monetary Fund and the World Bank publish GDP figures both at market rates and at PPP, with the PPP version frequently telling a different story about which economies are biggest. Because of this, PPP is central to ranking and comparing nations, and it connects to broader debates about trade and development, including the way [tariffs and trade barriers](/world/what-are-tariffs) distort the prices that PPP relies on. ## Why prices never quite line up PPP is a benchmark, not an iron law, and in the real world prices rarely match exactly. Several frictions get in the way. - **Non-traded goods and services.** A haircut, a restaurant meal or a hospital stay cannot be shipped across a border, so their prices can differ widely between countries without any market force pulling them together. - **Transport and trade costs.** Moving goods across the world is expensive, which keeps prices apart. - **Tariffs and barriers.** Taxes on imports and other restrictions deliberately drive a wedge between prices in different countries. - **Taxes and regulation.** Differing rates of sales tax, duties and rules change the final price on the shelf. - **Wages and rents.** Local labour and property costs feed into prices, especially for services, and these vary enormously between rich and poorer countries. Because of all this, economists treat PPP as a **long-run tendency** rather than a precise predictor of where exchange rates will sit on any given day. Over years and decades, currencies often drift toward their PPP values, but at any moment they can be far away from them. ## A simple worked example Suppose a fixed basket of goods costs £100 in Britain and the same basket costs $150 in the United States. The PPP exchange rate implied by that basket is £1 = $1.50, because that is the rate at which the basket costs the same in both places. If the market exchange rate happens to be £1 = $1.25, then by this measure the pound is **undervalued**: it buys more goods in Britain than its market value against the dollar suggests. If instead the market rate were £1 = $1.80, the pound would look **overvalued**. PPP gives you a yardstick against which to judge the market rate. ## The bottom line Purchasing power parity compares currencies by what they can really buy rather than by their market exchange rate, resting on the idea that an identical basket of goods should cost the same everywhere once converted. The Big Mac Index makes the concept tangible, and economists rely on PPP to compare living standards and the genuine size of economies more fairly than raw exchange rates allow. It is not an exact rule, because services, transport, taxes and trade barriers keep prices apart, but as a long-run benchmark it remains one of the most practical ideas in international economics. ## Frequently asked questions ### What is purchasing power parity in simple terms? It is a way of comparing money across countries by what it can buy. If the same basket of goods costs less in one country than another after converting currencies, that country's currency has more purchasing power. ### What is the Big Mac Index? It is an informal measure created by The Economist that compares the price of a McDonald's Big Mac across countries. Because the burger is broadly similar everywhere, differences in its price hint at whether currencies are over- or undervalued relative to PPP. ### Why do economists use PPP instead of exchange rates? Market exchange rates swing with trade and finance and do not reflect local prices for everyday goods. PPP adjusts for the cost of living, giving a fairer comparison of living standards and the real size of economies. ### Does PPP hold true in practice? Only loosely. Many services cannot be traded across borders, transport and taxes add costs, and barriers distort prices. So PPP is a long-run benchmark and a useful comparison tool, not an exact prediction of exchange rates. ## Sources - [International Monetary Fund](https://www.imf.org/) - [OECD](https://www.oecd.org/) - [World Bank](https://www.worldbank.org/) --- Daily Junction — https://dailyjunction.org/world/what-is-purchasing-power-parity