The 2017 Toyota Prius hybrid is an amazing machine. However, those here in the U.S. who discover that it has a 97.4 MPG rating in the U.K. need to know why that incredible-sounding MPG rating is no different than what the North American Prius actually earns.
With social media such as Facebook making it possible for club members from around the globe to communicate and share details on their favorite cars, it is worth remembering why U.K. vehicles always have such higher fuel efficiency ratings than the same models in the United States. There are really two reasons, and neither has anything to do with the technology of the vehicle.
U.K. Gallons Are Bigger
If you are not an engineering student or have not had a chance to visit the United Kingdom, you may not realize that a gallon is not the same unit of measure in the U.K. and the U.S. The gallon here in the United States is smaller. Torque News confirmed that indeed, the U.K. Prius will display "MPG or Miles Per Gallon", and that those are U.K. Miles per gallon. The conversion is roughly 1.2 U.S. gallons to one U.K gallon. So, without any other reason, the mileage in a U.K. vehicle will be about 20% higher than any U.S.-rated model. However, that is only part of the reason.
U.K. Ratings Are Not Equivalent to EPA Fuel Efficiency Ratings
In the U.S., we use the EPA's Combined, City, and Highway ratings. Almost every vehicle we test at Torque News (over 300 per year) do, in fact, match the EPA Combined fuel efficiency rating and many do better. The EPA has made its ratings harder and harder for automakers and the new testing, updated just last year, is very conservative.
However, the U.K uses other methodology. Its ratings are higher than the U.S. ratings. This is the largest factor in why the U.K. Prius earns a 97.4 MPG "Urban" rating, yet the same Prius Hybrid in the U.S. is rated at 54 City.