Fuel Consumption: What To Do With the Numbers (Updated for 2019)

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 www.fueleconomy.gov.

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.

Dave K

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It's free, it's fun, and it's wherever you are!

How to Measure Your Vehicle's Fuel Consumption (Updated for 2019)

To use less fuel you should know

how much you use now.

Fuel consumption numbers for your vehicle are something you could look up on a site like Natural Resources Canada or www.fueleconomy.gov. Those are the official Canadian and U.S. government sites for fuel efficiency ratings. But why use the government's numbers when it's much more satisfying -- and accurate -- to measure this yourself?

Earlier I suggested that when you drive, you should record your mileage and fuel purchases: this helps you to plan more and drive less. Today we refine your record-keeping and add to it.

Fuel consumption & fuel economy: cousins, not twins.

Now before we get all calculating, I'll be clear. We're looking at  fuel consumption, how much fuel you use to get around. That's related to fuel economy or fuel efficiency (they're, ahem, ... "reciprocal quantities") but not the same thing: look here >>>


Why do you want to know how much fuel you use?

Once you know your vehicle's fuel consumption, you can really commit to lowering it. The numbers make it real: measuring, recording and crunching the numbers makes them yours, so it's personal! Also, once you know fuel consumption you can convert it into fuel economy measures like mpg (miles per gallon) and mpg-imp (miles per imperial gallon). That helps you compare your vehicle to others in cases where they don't use L/100 km.  Plus it gives you another way of looking at how you use fuel. It puts your fuel use down on paper and motivates you to cut it back.

How do you do it?

First of all, keep recording your daily mileage and fuel purchases with that pen and paper (or booklet) you keep in the glove compartment. It's an on-going record of fuel use that lets you figure out your long-term average fuel use (such as a full year), zoom in on a specific time frame (like your summer vacation) or serve as data back-up if you mess up the cool technique I'm about to describe. The cool technique takes discipline and tight control over your vehicle's instrument cluster. And you have to keep your receipts. Are you ready for that?

I hear yes.

Cool Technique for Measuring Fuel Consumption

Start here.

Next time you buy fuel, fill 'er up. Do this every time you buy you buy fuel, forever.

Fill 'er up. Every time.

Now do this...

On the back of the receipt write down how many litres of fuel you bought and your total mileage. In this example total mileage is 141 577 km. Now look at the other number, 415.0 km. That's trip mileage, and the first time you do this it's meaningless: you can't use it. But you'll need it every time after this, so starting next time write it down too.

Total mileage is 141 577 km. Trip mileage is 415.0 km.

 then do this ...

 We need to reset the trip counter to 0 so it can start measuring how far you drive. This usually means holding in the long button next to the display until the number goes to 0.

Reset the trip counter to 0 by holding this button in.

... and you're ready!

From here onward, every time you buy fuel remember these points, in this order:

1. Always fill the tank.
2. Record how many litres you bought, total mileage and trip mileage. Either on the receipt or in the booklet.
3. Reset the trip counter after you get the mileages, and before you leave the gas station. Every time.

So that's the cool approach to measuring fuel consumption, and we're done for now. Next blog I'll explain how to use the numbers you wrote down. You'll be a fuel consumption Jedi!

Dave K

Btw, there's still time to join us for Getting There Green Day 2019.

It's free, it's fun and it's for a great cause!