Counterfeit currency rates are determined by part per million (PPM), which reports how many counterfeit money notes are found in circulation.
The United States has as PPM of 6.5 PPM, meaning that authorities discover 6.5 counterfeit banknotes that have been passed as real currency out of every 1 million banknotes.
Australia has a rate of 6.8 PPM, and Mexico has a rate of 83 PPM.
G-20 nations use a PPM benchmark of 50 as to whether or not the country’s currency system can be considered secure.
Source: Grant Robertson, “Funny money: How counterfeiting led to a major overhaul of Canada’s money,” Globe and Mail, December 3, 2011.