To a brighter future

To a brighter future

Saturday, March 17, 2012

Fuel Consumption: what to do with the numbers (updated for 2017)

If you know your numbers you'll want to make them better.

Last time I showed you a cool technique for measuring fuel consumption. Now we play with those numbers, which is even more cool, because who really does enough math? But I have to warn you: some images may disturb sensitive drivers. You're about to figure out how much fuel you burn getting around and how much carbon dioxide you leave in your wake. Now for the faint of heart! The good news is that seeing these numbers will probably inspire you to cut down on fuel and CO2 so that we all get a happy Hollywood ending.

To recap, you've been:
  1. filling the tank each time you buy fuel
  2. writing down litres bought, total mileage and trip mileage each time you buy fuel
  3. resetting the trip counter before you leave the gas station, every time
Nice work. Let's get calculating!

You've been writing this stuff down, somewhere.

 We'll start with the basic one, fuel consumption. When I do this I work from the receipts, which I always keep. You may just as easily be working from that driving log booklet you keep in the glove compartment. What matters is that you have
<<< this info:

If you've made a boo-boo and forgotten to record your trip mileage, all is not lost. You can get it by subtracting your total mileage from the total mileage on the receipt from the fill-up before this. Good thing you're writing it down!

Got the calculator ready? Divide the number of litres you bought by the trip mileage. Now multiply the result by 100.

A simple example, from the Land of Easy Math.

Done! You've just calculated your vehicle's fuel consumption between this fill-up and the one before, in

litres per 100 kilometres.

Just like the example  >>>

So after doing that, "are you frightened? Not nearly frightened enough!" (it's from some movie) Perhaps your number is really low, like the example, which is from my diesel standard-shift Golf. Lots of vehicles will give results between 6 and 10 L/100 km. Below this range your vehicle's fuel use could be called  Really Quite Good; above it, would be, well ... Really Not So Good. I'm being somewhat arbitrary, and maybe a bit smug --  diesel standard-shift Golf  -- so if you'd like to make comparisons try Natural Resources Canada or

But if, as Aragorn said, you're "not nearly frightened enough" by that number let's try another one. Carbon dioxide is the second-most abundant greenhouse gas in the atmosphere, and being number two it tries harder: it's becoming more abundant over time due mainly to anthropogenic sources, Your vehicle, and mine, are anthropogenic sources. So let's figure out how much CO2 our vehicles emit, starting with mine.

My Golf' may not have feet, but it has a carbon footprint.

To turn the fuel consumption number for my diesel Golf into carbon dioxide released, simply multiply it by 2.7 ... as in diesel engines typically release about 2.7 kilograms of carbon dioxide per litre of fuel burned (2.7 kg CO2/L). >>>

Gas-buring vehicles have a carbon footprint too.

Now it's your turn. If you managed to get the same fuel comsumption of 5 L/100 km, but with a gasoline-burning engine, your numbers would look
<<< like this.

Except you probably wouldn't get those numbers. Diesel engines release more CO2 per litre, but they use a lot less fuel, roughly 65% of what a comparable gas engine uses. So between diesel and gas, diesel is usually the better choice for a smaller carbon footprint.

Is the math over yet? Not quite -- one more conversion for you. A magical way to turn fuel consumption into fuel economy, to make you fluently bilingual in both litres and mpgs.
Do you speak mpgs?

The two slides spell it out. If you were born and raised in L/100 km but want to converse in miles per gallon, go here >>>

It takes longer to say it in L/100 km.

And if your first tongue is mpgs but you want to speak litres like a native,
<<< go here.

Okay, math time is over! This is a starting point for reducing your fuel use, a real-world handle on part of your environmental impact. Reducing it not just by driving more efficiently, but also by making non-car choices. Now that you know your numbers you can do something about them. Sort of like cholesterol.

In Planning for Getting There Green - Part 3 we explore those other two planning tools, weather forecasts and shopping lists. Without all the math.

Dave K

Join us for Getting There Green Day 2017?
It's free, it's fun, and it's wherever you are!