Lifetime MPG

This is a manual calculation derived from keeping records of the miles per gallon obtained for all tank fill-ups, either calculated by the car or in the traditional way by the owner. The Prius has an board computer which calculates mpgs based on the amoung of gas injected into cylinder 1 times 4. This is accurate enough for me, so I don't bother doing the old calculations. I consistently get an average of 51 mpgs.

 

Averaging your individual tank mpg readings is accurate only if you factor in the distance driven on each tankful.

The only way to know your lifetime mpg on the Prius is to record the amount of gas pumped every time you fill up, and keep a running total, and divide that into your total miles driven. The figure will be only as accurate as the gas pumps and your odometer, and will be inaccurate for the first few tanksful as the tank may not be filled to exactly the same level each time.

Some cars offer a readout of lifetime mpg. The Prius does not.