Calculation of average fuel consumption of a car: formulas and methods

Why control fuel consumption

Every car owner is faced with the need to plan a budget for vehicle maintenance. One of the main and regular expense items is the purchase of gasoline or diesel. Knowing the exact appetite of your car allows you not only to correctly calculate the cost of long trips, but also to notice technical faults in time.

If the car suddenly begins to consume 2-3 liters more than usual with the same driving style, this is the first signal to contact a service center. The cause may be worn spark plugs, clogged filters, or problems with the fuel system.

Universal mathematical formula

Around the world (except in countries that use miles and gallons), the standard for measuring a car's fuel economy is the number of liters the engine burns over a distance of exactly 100 kilometers.

To calculate this indicator, a basic arithmetic proportion is used:

Practical example: You drove 350 kilometers by car. During this time, the engine consumed 28 liters of fuel.
We count: 28 divided by 350 (we get 0.08). Then multiply 0.08 by 100.
Bottom line: your average is 8 liters per 100 km.

Full tank method: the most accurate test

The on-board computers of modern cars often underestimate the actual figures by 5-10% in order to show the car as more economical. To obtain absolutely reliable data, experienced drivers use the gas station measurement method.

1. First refueling. Come to the gas station and fill the tank to the very edge (before the first “shoot” of the gun). Immediately after this, reset the daily odometer (mileage counter) on the dashboard.
2. Normal operation. Drive along your usual routes. It is advisable to remove more than half the tank - for example, drive 200 or 300 kilometers. The greater the distance, the more accurate the final result will be.
3. Second refueling. Return to the same gas station (preferably even the same column) and fill up again until the tank is full.
4. Fixing data. Look at the receipt: the number of liters filled now is exactly the fuel that you spent. Look at the instrument panel: the exact distance is indicated there. Plug these two numbers into the formula above.

What determines the indicators on the dashboard

The numbers declared by the manufacturer in the service book are obtained in ideal laboratory conditions: the car is driving on a level stand, without wind, with the headlights turned off and the interior empty. In real life, many factors influence the motor’s appetite:

• 🚦 Driving mode. In city traffic jams, with constant acceleration and braking at traffic lights, the car always burns 20-30% more than when moving evenly along the highway.
• ❄️ Weather conditions. In winter, a lot of energy is spent on warming up the cold engine and interior, as well as on overcoming snow porridge. Additional resistance increases the load on the motor.
• 💨 Aerodynamics. Opening windows at speed, installing a roof rack (even empty) or driving with a trailer disrupts the streamlining of the body.
• ⚡ Electrical appliances. The switched on air conditioning or climate control takes away part of engine power on yourself, steadily adding from 0.5 to 1.5 liters to the total per hundred.

Comparison table of operating modes

To understand what figures are the norm fuel consumption, check out the average coefficients for passenger cars of class “B” and “C” (engine capacity 1.6 liters).