How to calculate fuel consumption
To calculate your vehicle's actual fuel consumption you need to know two numbers: the distance traveled and the amount of fuel used to travel that distance.
Here is one easy way to calculate fuel consumption:
- Fill up your tank to the first click-off and reset the trip odometer to zero.
- Drive.
- Next time you come to a gas station for a fill-up, write down your trip odometer readings, fill the tank the same way, to the first click-off and write down the amount of fuel it took. Now you've got what you need - the amount of fuel used and the distance travelled between fill-ups. For more precise results, use numbers of fuel used and distance travelled between three or more fill-ups.
To calculate your MPG, divide the total number of miles driven by the number of gallons used:
For example: You filled up your tank and zeroed the trip odometer. Next time you at the gas station, your trip odometer shows 320 miles and it took 18.5 gallons to fill up the tank again. That means your car consumed 18.5 gallons to drive 320 miles. To determine how many miles per gallon you are getting, divide the distance driven by the number of gallons used:
320 miles / 18.5 gallons = 17.3 MPG
For Metric System, you need to multiply the number of liters by 100 and then divide by the kilometers driven.
The formula is:
For example: You filled up your tank and zeroed the trip odometer. Next time you at the gas station, your trip odometer shows 480km and it took 42 Liters to fill up the tank again. That means your car consumed 42 liters to drive 470 kilometers, or its fuel economy is:
42L x 100 / 470 = 8.9 L/100km
Once you know what your car's actual fuel economy is, you may want to compare it to what it should be.
You can find an estimated fuel economy rating for your car at: Fueleconomy.gov.
If your actual fuel economy is significantly worse than estimated numbers, this could be an indication of some problem with your car, such as: dirty air filter, bad oxygen sensor, clogged or leaking fuel injectors, bad spark plugs, low compression, wrong timing, faulty thermostat, under-inflated tires, dragging brakes etc.
