Fuel Consumption Calculator ⛽

1. Fuel consumption formula
2. Different ways to calculate fuel economy
3. How to achieve better fuel efficiency?

    Fuel consumption formula

The formula for calculating fuel consumption used in this online fuel consumption calculator is:

Fuel consumption = Fuel used / Distance travelled

The result depends on the metrics used as input: miles per gallon if the input was in miles and gallons, and km per liter if the input was in kilometers and liters.

Additionally, the fuel consumption calculator will output the fuel cost per mile or fuel cost per km, depending on the metric units selected, as well as miles per $ / km per $. These are very useful when estimating your fuel costs and can help you predict your expenses easier on a future trip. For example, if you notice that your usually spend $0.15 per mile (15 cents per mile), then if you know you will be travelling for 200 miles, you can calculate the cost of the trip by multiplying 200mi x $0.15 = $30 for a 200 mile trip. Similarly, for km.

    Different ways to calculate fuel economy

Fuel efficiency, or fuel economy, can be a tricky concept. Understanding that is key for the correct interpretation and comparison of gas consumption estimates such as those produced by this calculator.

For example, say you want to compare two types of cars: A and B. You put two researches, one American and one French, to the task, with the first using kilometers per liter as an efficiency metric, while the second using liters per km. You have each researcher record the efficiency of 2 cars of each type, or, alternatively, the consumption of one and the same car in two different environments (the data available is the same for both), and the results recorded by them look like so:

Data for car type A:

Researcher	Car 1	Car 2	Average
American (km per liter)	1 km/l	4 km/l	2.5 km/l
French (liters per km)	1 l/km	0.25 l/km	0.625 l/km

Data for car type B:

Researcher	Car 1	Car 2	Average
American (km per liter)	2 km/l	2 km/l	2 km/l
French (liters per km)	0.5 l/km	0.5 l/km	0.5 l/km

Average above means the arithmetic mean. The US engineer will see that for type A the average is 2.5 while for type B it is just 2.0, concluding that type A is more efficient than type B as it can cover a greater distance with a liter of diesel, petrol, gas, etc. The French will see that for type A the average is 0.625 while for type B it is 0.5 and will conclude that type B is more efficient than type A, as the car will use less fuel to cover the same distance. The two researchers would come to different conclusions as they are using different metrics!

But who is right in the above example? The fuel consumption calculation is correct in both cases. The issue is what we care about when we calculate fuel consumption and fuel efficiency / fuel usage. Most people would argue that we care about how much fuel we would need to cover a given distance. In such a case the French researcher is correct as the average is misleading the US researcher. Here is an explanation why: if you take both cars of type A and want to cover 100 kilometers with each of them, you would need not 200 / 2.5 = 80 liters, but 125 liters of petrol (100 liters for the first car and 25 liters for the second). The French will get it right by multiplying 200 x 0.625 = 125. For type B both researchers will correctly estimate that 100 liters will be required for the same task. Therefore, type B is more efficient than type A.

However, if you define efficiency as covering the greatest distance given a certain fuel amount, then the US researcher would be correct. If we give each car of type A a liter of fuel, they will cover 5 kilometers combined while giving each car of type B a liter of fuel, they will cover only 4 km combined. It follows that type A is more efficient than type B using this definition. Note that the km/l average is not misleading here, as it is 2.5 km/l, and 2 x 2.5 = 5, which is correct.

The above is an illustration of why when using our fuel consumption calculator or similar tools it is important to keep track of the end goal and define the question at hand precisely before measuring and making conclusions. It is also a lesson on applying appropriate data transformations. The arithmetic average is not invariant to monotonic transformations which becomes an issue when averaging the performance of two or more vehicles or when averaging the performance of a single vehicle in different situations. For example, highway fuel consumption and city drive consumption could be used in place of Car 1 and Car 2 in the example table above and produce the same result.

The car example uses as a basis one from Hand D. (1994) "Deconstructing Statistical Questions", Journal of the Royal Statistical Society, Series A, Vol.157-3:317-356. Fuel consumption calculations are performed using this online calculator.

    How to achieve better fuel efficiency?

In brief, the best way to achieve better fuel economy is to:

1. Keep your car and tyres well-maintained
2. Avoid frequent acceleration and deceleration
3. Drive at a lower overall average speed
4. Avoid or reduce the use of air conditioning
5. Reduce the weight of the vehicle by not carrying excess cargo

All of the above would reduce the amount of fuel consumed per unit of distance covered. For more in-depth advice, check out our list of ways to improve your fuel economy.