Why vehicle fuel consumption figures are inverted

By MUNGAI KIHANYA

The Sunday Nation

Nairobi,

30 November 2025

A reader who prefers anonymity asked me to comment about on the fuel consumption figures displayed in different cars. He has noted that in a Mercedes, the numbers are given in litres per 100km while in a Toyota, they are kilometres per litre. He wants to know why there is a difference and also how to compare the two.

We have grown accustomed to seeing fuel consumption expressed in number of kilometres per litre. Perhaps this is an intuitive quantity: if you put, say 5L of fuel (one jerrycan) into a car that does 10km/L, you can easily estimate that it will go for about 50km. (You simply multiply10km/L multiplied by 5L).

However, as I noted in these columns in May 2021, kilometres per litre can be confusing when comparing the consumption rate of two cars. Suppose one car does 10km/L and another one does 15km/L: which of the two has higher consumption? Of course, the answer is the first one (10km/L).

But when you think about it, the number 10 is LOWER than the number 15; why then do we say that 10km/L is HIGHER consumption rate than 15km/L? Do you now see the contradiction? For this reason, some manufacturers (especially European ones) prefer to indicate the figures in L/100km.

Thus, the car running 10km/L will indicate 10L/100km while the one doing 15km/L will show 6.7L/100km. Now we can clearly see that the first car has a HIGHER consumption rate since the number 10 is BIGGER than the number 6.7.

Unfortunately, this style might be a little awkward when estimating the amount of fuel needed for a journey. For example: if you know that your car runs at 15km/L, how much fuel will you need to do a 120km journey? To get the answer, you divide 120 by 15; the result is 8L.

If, on the other hand, the consumption was given as 6.7L/100km; then you multiply 6.7 by 120 and then divide by 100. The answer comes to the same 8L as before. Obviously, it appears more involving than the single division of the previous method. For that reason, it might be better for car manufacturers to display the consumption in litres per kilometre (L/km); thus, 0.067L/km instead of 6.7L/100km. Better still, 67mL/km.

Now, 15 is a nice round number while 6.7 seems like a cumbersome decimal value. The reality is that no car a consumption rate of a nice round number! It may be an awkward figure like 15.38km/L. This converts to a better sounding 6.5L/100km.