Fuel Economy Calculation and Conversion

Calculate Miles per Gallon

I already put together a little post on how to calculate your fuel economy in miles per gallon (MPG), but not everyone is interested in that particular measurement. That's 'cause there are only a few countries who use the imperial system of measurement (feet, quarts, miles and gallons), so the phrase "miles per gallon" doesn't mean much to people who live outside the USA. 

Calculate Liters per 100 km

In most of the countries that use the metric system, people share their fuel economy with a number called l/100km, or liters per 100 kilometers instead of the MPG so familiar to people in the States. You just need two numbers to calculate l/100km, though the division is a little different from what you're used to.


The first number you'll need to know is the distance between fill-ups (fuel economy calculation is only accurate if you fill the tank each time). You can get this number from the trip odometer on your instrument panel or by writing the mileage on the gas station receipts and subtracting the last odometer reading. The second is the number of liters consumed. Get that number from the receipt or by reading it off the pump. Don’t try to use your fuel tank capacity from the owner’s manual, because you’ll underestimate the fuel economy (the tank wasn’t really empty, was it…)

Now, to calculate: just divide the fuel consumption by the distance. Don’t forget to convert the distance to 100s of km first. For example:

89.50 liters ÷ 1125 km driven (11.25 hundreds) = 7.96 liters/100 km
250.9 liters ÷ 2020 kilometers driven (20.2 hundreds) = 12.42 liters/100 km

This system is the opposite of MPG, where big values are preferable. In l/100km, a small number is better than a big number. For comparison, a value of 7.96 l/100km is the equivalent of 29.55 MPG, while a value of 12.44 is about 18.9 MPG.

Here: try this little gadget...

Kilometers Driven:
Liters Used:

Your Fuel Economy: 
Another Stoopid GOOGLE GADGET

Converting between MPG and l/100km

If you have a calculator or still remember how to do simple math, it's not hard to convert between miles per gallon and liters per 100km: 

Miles per gallon = 235.2 ÷ liters per 100 km 
 -- for example, 11.92 l/100km = 19.73 MPG
And liters per 100 km = 235.2 ÷ miles per gallon
 -- for example, 25.5 MPG = 9.22 l/100 km

If you don't have a calculator handy and you've forgotten how to do long division, try this handy little gadget:

Fuel Economy:


Converted Fuel Economy: 
Another Stoopid GOOGLE GADGET

Have fun - and never let me hear you talking about "dollars per fill-up" again!