Guide
How to calculate gas mileage
Two full tanks and the odometer are all you need. Here is the method, and the traps.
The full-tank method
- Fill the tank to full and note the odometer.
- Drive, then fill to full again and note the odometer and the gallons.
- mpg = miles driven between the two full tanks ÷ gallons of the second fill-up.
Example
Full tank at 52,000 miles. Next full tank at 52,330 miles, taking 10 gallons: 330 ÷ 10 = 33 mpg.
Partial and missed fill-ups
A partial fill-up in between is added to the next full one: 4 gallons at 52,150, then 6 gallons to full at 52,330, still 330 ÷ 10 = 33 mpg. A fill-up you forgot to note breaks the count: that cycle must be left out, or the mileage looks far better than it is.
Other units
L/100 km = 235.2 ÷ mpg (US): 33 mpg is about 7.1 L/100 km. A UK gallon is larger than a US one: 33 mpg (US) is about 39.6 mpg (UK).
With Car Log
Enter each Fill-up with Full tank or Partial; tick Missed fill-up when one was not logged. The app shows the consumption of each cycle and the average, with its period. See Fuel log.
