In-depth
Fuel Consumption Calculator: km/l, l/100km, and Trip Cost
Knowing the actual fuel consumption of your car is essential for planning trips, managing your budget, and comparing different vehicles. This calculator lets you compute km/l, liters per 100 km, and the estimated cost of a trip based on fuel price.
km/l vs l/100km: which unit to use?
In Italy and across Europe, there are two ways to express fuel consumption:
| Unit | Meaning | Where it's used |
|---|---|---|
| km/l | How many km per 1 liter | Italy (informal) |
| l/100km | How many liters needed for 100 km | Europe (spec sheets) |
| mpg | Miles per gallon | USA, UK |
Quick conversion: l/100km = 100 ÷ km/l. For example, a car that does 15 km/l consumes 100 ÷ 15 = 6.67 l/100km.
How to measure actual fuel consumption
The manufacturer's stated consumption is measured under laboratory conditions and rarely matches reality. To find out your actual consumption:
- Fill the tank completely and note the mileage (or reset the trip odometer).
- Drive normally until the tank is almost empty.
- Fill up again and note the liters added and the kilometers driven.
- Calculate: km/l = kilometers driven ÷ liters added.
Example: you drove 520 km and added 38 liters at the refueling stop. The consumption is 520 ÷ 38 = 13.7 km/l (or 100 ÷ 13.7 = 7.3 l/100km).
Calculating the cost of a trip
The formula for estimating the fuel cost of a trip is:
Cost = (Distance in km ÷ km/l) × Price per liter
Or: Cost = (Distance ÷ 100) × l/100km × Price per liter
| Trip | Distance | Consumption | Fuel price | Estimated cost |
|---|---|---|---|---|
| Milan – Rome | 575 km | 6.5 l/100km | €1.85/l | €69.14 |
| Rome – Naples | 225 km | 7.0 l/100km | €1.85/l | €29.14 |
| Turin – Florence | 420 km | 6.0 l/100km | €1.80/l | €45.36 |
| Bologna – Venice | 155 km | 7.5 l/100km | €1.85/l | €21.51 |
Factors that affect fuel consumption
Actual consumption can vary significantly based on several factors:
- Driving style: harsh acceleration and high speeds can increase consumption by 30-40%.
- Type of route: city driving consumes much more than highway driving at a constant speed.
- Air conditioning: A/C can increase consumption by 10-15%.
- Tire pressure: underinflated tires increase rolling resistance and fuel consumption.
- Load: every extra 100 kg increases consumption by about 5%.
- Maintenance: dirty filters, old oil, and worn spark plugs reduce efficiency.
- Speed: above 120 km/h, aerodynamic drag increases exponentially.
Tips for saving fuel
- Smooth driving: anticipate braking, accelerate gradually, and maintain a constant speed.
- Higher gears: shift gears between 2,000 and 2,500 rpm (diesel) or 2,500-3,000 (gasoline).
- Check your tires: verify tire pressure at least once a month.
- Reduce weight: remove unnecessary items from the trunk.
- Turn off the engine: for stops longer than 30 seconds, Start&Stop saves fuel.
- Plan your route: avoid heavy traffic where possible.
- Highway speed: driving at 110 km/h instead of 130 km/h reduces consumption by up to 20%.
How to use the calculator
Enter the kilometers driven and the liters of fuel consumed to get the consumption in km/l and l/100km. Add the price per liter to also calculate the cost per kilometer and the total trip cost. You can also enter the distance of a future trip to estimate how much fuel and money you will need.
