i find this idea fascinating, it’s the modern equivalent of asking how many loaves of bread something cost

Big Mac Index

Burgernomics is based on the theory of purchasing-power parity, the notion that a dollar should buy the same amount in all countries. Thus in the long run, the exchange rate between two countries should move towards the rate that equalises the prices of an identical basket of goods and services in each country. Our “basket” is a McDonald’s Big Mac, which is produced in about 120 countries.
The Big Mac PPP is the exchange rate that would mean hamburgers cost the same in America as abroad. Comparing actual exchange rates with PPPs indicates whether a currency is under- or overvalued.

via the economist

while i was looking for a picture, i discovered that in different countries, Big macs have different recipes and calorific values. A US ‘mac has 540 calories and an Australian one has 48. (wikipedia)