With increasing prices at the pump, fuel consumption is becoming more and more important. Knowing how much gasoline your vehicle consumes over 100 kilometers (l / 100 km) can help you determine its appetite and its impact on your wallet. Understanding how to calculate this average consumption is useful for estimating many other parameters. This will allow you to calculate how a € 0.1 increase at the pump affects your budget, see how much lower fuel consumption saves you per month, or determine if your vehicle is consuming more than it should and consider repairing it.
Steps
Part 1 of 4: calculate the average fuel consumption of a vehicle
Step 1. Go to a gas station and fill your fuel tank
It can cost money, but it is the key to getting an accurate result.
Step 2. Record the mileage
Before you even step away from the pump, write down your current total mileage. We call it mileage A.
Step 3. Drive normally
To get as accurate a reading as possible, drive until the tank is at least half empty. The more distance you can travel before refueling, the better.
Step 4. Fill the tank again
Try to go to the same gas station and use the same pump as the first filling. Pumps can indeed be calibrated differently. This time, pay attention to the number of liters needed to fill the tank. This is normally indicated on the pump. We call this data liters.
Step 5. Record the mileage again
We call her this time mileage B.
Step 6. Do the math
The formula for determining the average consumption is as follows.
 Consumption in l / 100 km = (liters x 100) ÷ (mileage B  mileage A).
 Deduct mileage B from mileage A. This operation gives you the mileage since the last filling.
 Multiply the amount of fuel consumed (Liters) by 100. Then divide by the mileage driven to get your average fuel consumption.
Part 2 of 4: Examining practical cases
Suppose you want to track the average fuel economy of a car with 35,000 km on the odometer with a full tank at the start.
 Route A: 37.05 l needed to refuel at 35,650 km
 Route B: 28.6 l needed to refuel at 36,170 km
 Course C: 34, 16 l needed to refuel at 36,780 km
Part 3 of 4: Calculate average consumption
 Course A: (37.05 x 100) ÷ (35,000  35,650) = 5.7 l / 100 km
 Route B: (28.6 x 100) ÷ (35 650  36 170) = 5.5 l / 100 km
 Course C: (34, 16 x 100) ÷ (36 170  36 780) = 5, 6 l / 100 km
Part 4 of 4: Take additional details into account
Step 1. All modern cars are equipped with a trip meter
This is a resetable odometer. This is complementary to the regular odometer, which indicates the total mileage traveled by the car since it was put into service. To determine a distance traveled, you can therefore also reset your trip meter to zero and read the mileage at the end of the trip.
Check your meter. Not all cars provide an accurate odometer reading. This will not only give you an approximate value of the distance traveled, but also an incorrect average fuel consumption result. Many roads are punctuated by kilometer markers. Take a section of road equipped with terminals for several kilometers
Step 2. Choose a departure terminal
Reset your daily counter by going to the terminal.
 Choose an arrival terminal. At the end of the course, write down the number on the meter. An accurate meter will show the same value as the mileage difference between the two terminals.
 If your meter shows a number lower than the distance traveled, your actual average consumption will be better than what you calculated. You are actually traveling farther than your meter tells you. Conversely, if this indicates a figure greater than the distance traveled, your actual average consumption will be worse than that calculated.
Step 3. Calculate the offset
Let's call the actual distance traveled “R”, and the odometer reading “C”. We call "D" the difference index. The formula to determine this index is:
 D = R ÷ C.
 For example, if you have driven 5 kilometers between the terminals and your odometer reads 4.5 km, the formula reads as follows.
 D = 5 ÷ 4, 5 or 1, 11. To obtain the actual mileage to be used in the average consumption formula, multiply your measured mileage by 1.11 before continuing your calculation.
 If mileage B  mileage A = 100 km, multiply it by D (1, 11). In this example, you have actually driven 111 km.
 If your odometer shows 5.5 km driven, the formula reads as follows.
 D = 5 ÷ 5, 5 or 0, 91. Again, you must multiply the difference between mileage B and mileage A by D.
 If mileage B  mileage A = 100 km, multiply it by D (0, 91). In this example, you have only done 91 km.
Advice

To get the most out of your fuel, drive between 50 and 90 km / h. Not only you will pay less fuel, corn you will extend the life of your vehicle and its components.

You can use your average drink to experiment with ways to save fuel.
For example, if you normally drive at an average speed of 80 km / h, calculate your average consumption, then try to drive at 70 km / h on average and calculate your consumption again. You will likely notice a difference.
 Calculate your average consumption several times to refine your measurement. If you make a long trip at a cruising speed on the national highway, your consumption will decrease. On the other hand, if you drive around town, by increasing the number of stops and starts, your average fuel consumption will increase.
 The vast majority of cars are equipped with an odometer which can be reset to zero. This instrument comes in addition to the usual odometer which totals the total mileage driven. You can use it to measure the distance traveled by your car. Divide the capacity of the fuel tank by the number of kilometers traveled corresponding to a full tank to obtain the consumption of the car.
 To see how a change in fuel prices can affect your budget, take the mileage you expect to get in a week (or a month, or a year), divide it by 100, and multiply it by your average consumption. Then multiply the result by the price of the current liter. By applying other prices, you will see how much your spending will increase or decrease per week (or per month, or per year).
Warnings
 Your calculations may be inaccurate. Repeat the operation 2 or 3 times and average the results to obtain the most accurate average consumption possible.
 Consumption varies with driving style. Limiting unwanted braking and accelerating will improve your fuel consumption. If you are used to driving in the city, you will therefore see your fuel consumption decrease as you adopt a cruising speed on the country road.
 In other countries, this data may change. In the United States, the units are different and the average fuel consumption is expressed in miles per gallon (MPG). In the United Kingdom, fuel is sold by the liter, but consumption is given in miles per imperial gallon. This peculiarity dates from the adoption in 1965 of a particular metric system, confusing it with the American system.