Wealthy Maths: How to calculate fuel consumption

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The petrol price is a common gripe amongst South Africans, and with the latest petrol price hike, it might be more useful than ever to know your car’s fuel consumption.

So how do you calculate it?

There are two measures of fuel consumption – litres per 100km (l/100 km) and kilometre per litre (km/l). In this article, you will learn how to calculate both.

Some of the newer, fancier cars are super smart, enabling you to get your consumption with the click of a few buttons on the steering wheel. Everyone else will need some basic arithmetic.

  1. Set your starting point. The next time you go to the petrol station, ask the petrol attendant to fill up to auto-stop. The reason you ask for auto-stop is to set a defined level. Reset your car’s trip/distance counter to 0.
  2. After you leave the petrol station, drive as you would usually do. Just don’t reset your trip/distance counter.
  3. When refueling, ask the petrol attendant to fill up to auto stop again. Check the petrol pump to see how many litres went in. Check your trip/distance counter and note the kilometre reading.

You now have the two pieces of information you need to determine your fuel consumption – the number of litres used (from the petrol pump reading) and the number of kilometres you travelled (from your car’s trip/distance metre).

For example, let’s say your car used 18.5 litres and travelled 254km.

Litres per 100km

Take the litres used, divide it by the distance travelled and multiply it by 100.

Fuel consumption = (18.5/254) x 100 = 7.28 litres per 100km.

This means your car uses 7.28 litres to drive 100km. You can also calculate the cost of fuel to drive 100km. In this example, at an inland petrol price of R16.85/litre, it would cost you R122.67 to drive 100km.

Kilometre per litre

Take the distance travelled and divide it by the litres used.

This means that one litre of petrol enables your car to drive 13.73km.

As a cost-saving exercise, why not make a game of it? Drive as fuel efficiently as possible (ex. no speeding towards red traffic lights and cruising at a constant speed on the highway) and see how low you can get your consumption. A nice side effect fuel-efficient driving is more money in your wallet each month.

Wealthy Maths blog

Our friend Stealthy Wealth knows his way around maths. Luckily for us he also speaks human, which is why we asked him to explain the most important maths we need to know to be good at money. This is not your average maths class. Tune in once a month and turn into a money mathemagician.

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