1. Go to the gas station and fill up the fuel tank.
- Record the mileage, before even pulling away from the pump. We will call this Mileage A.
- Drive normally until the tank is less than half full.
- Fill up the tank again (preferably at the same station using the same pump as pumps may be calibrated differently). This time, pay attention to how many gallons it takes to fill up the tank. This is usually shown at the pump.
- Record the mileage again, just like before. We will call this Mileage B.
- Subtract Mileage A from Mileage B. This will give you the number of miles you drove since your last fill-up.
- Divide your answer by the number of gallons it took to fill up your tank. This will give you your car's MPG.