The Heinlein Index is the answer to the question:
For how many minutes must a journeyman carpenter [that is, neither an apprentice nor a master] labor in order to be able to buy one additional kilogram of the local standard bread?
For the United States, 2000 data (the most recent I can easily find) shows the median hourly wage of a journeyman carpenter as USD 17.28, and a loaf of bread (approx. 1 lb = 1/2.2 kg) costing USD 2.50. That leads to a current HI of about 19.
The neat thing about the HI is that it represents the marginal relative value of labor, and thus neatly compensates for not only the varying cost of living, but the varying standard of living. We all have to eat, though some of us live in caves and others in high-rises.