The actual formula to get km per litre is 100 divided by 8 = 12.5, meaning that your car will give you 12.5 km on one litre.
most cars are issued with a nifty little piece of equipment called a trip computer. Most modern trip computers will record, calculate, and display the distance travelled, the average speed, average fuel consumption, and instant fuel consumption. In most cases, it will tell you your range, ie. how many more kilometres you can travel before you need to fill up. However, if your car is slightly older and without a trip computer, you will have to rely on simple mathematics to get a more realistic idea.
Also, if you go according to the manufacturer’s consumption figures, remember that they are (mostly) a little optimistic. When they tell you it’s 5.0 litres per 100 km, you can almost add 2 litres to that figure for a more realistic idea of fuel economy. In some cases it’s not a huge difference, so don’t use this as a rule of thumb. For the purposes of this article, I will be using the Suzuki Baleno as a practical example to assist in my explanation.
Kilometres litres per 100 km
As a journalist, I work with litres per 100 km, but many people understand the km-per-litre system better. In the US and UK, it’s miles per gallon or MPG – yet the two countries have different gallon sizes!
If litres per 100 km figures don’t make sense to you, you can use an online converter to find out how many kilometres you’ll get on one litre of petrol, and vice versa. Or, you can just do a simple calculation as per the table below.
To convert Formula to use
|km per litre to litres per 100 km||divide 100 by km per litre|
|litres per 100km to km per litre||divide 100 by litres per 100 km|
Estimating the fuel cost for a trip
I love a road trip and am always looking to save money on fuel (so I can spend it on food), so I usually work out my petrol budget to the last kilometre.
To estimate the fuel cost for a trip you need the trip distance, cost of fuel per litre, and the vehicle’s average fuel consumption.
In other words: Divide the total distance (km) by 100. Now multiply the answer by the average fuel consumption, and then multiply this number by the price of fuel (per litre).
Let’s say I want to travel from Cape Town to East London, which is a distance of 1040 km. I will be using the above-mentioned Suzuki Baleno because it’s light on fuel. To make this calculation, I will use the average fuel consumption of 5.8 litres per 100 km, but then I also have to take into consideration that I probably won’t be driving 90 km per hour in perfectly flat, windless conditions. So I will base my calculations on 7.0 litres per 100 km – I’d rather be a little conservative so I’m not out of pocket should I encounter typhoons blowing against the front of my windscreen – hopefully not!
Ok, here goes. My Baleno will use 7.0 L/100 km. So the first step is 1040 km (the distance) divided by 100 which equals 10.4. Now I will multiply this by 7 which equals 72.8 litres.
This figure of 72.80 l will now be multiplied by the current petrol price. I used the current price (93) at the coast which is R 21.34 (correct on the 10th of July 2023) which amounts to R 1 553,55. Should you plan on coming back, double that figure, but don’t forget about the kilometres you’ll be covering while you’re there!