You can't calculate exact inflation (or at least I don't know how you would). You are conflating our government's definition of inflation with a general definition of inflation. The U.S. government calculates inflation using a certain formula (more specifically, the consumer price index). Other countries do it differently. They are indexing it indirectly by looking at prices of certain goods and services. It's accuracy as a measure of inflation (or cost of living indicator which is what it really is) is debatable.