That’s all the scientific stuff. When I pick up a test vehicle, I make sure it’s full and note the mileage. I then drive it for a week, pretty much as a regular owner would: on the highway and on urban streets, running errands, throwing stuff into the trunk, and keeping up with traffic without seriously bending the law. I try to adjust my driving to the vehicle’s intended purpose, pushing sports cars harder than I do the small grocery-getters. I fill the tank with the recommended fuel grade when returning the car (or as needed throughout the week, if I drive it enough), mark my mileage again, and then figure out the consumption.

To do that, I multiply the number of litres pumped in by 100, and then divide that number by the number of kilometres driven. For example, if I drove 300 kilometres and used 32.5 litres, I’d multiply that by 100 to get 3,250 litres. Divided by the 300 km, it works out to 10.8 L/100 km. To turn that into Imperial miles per gallon – not the U.S. type, which uses a different size gallon – divide 282.48 by the metric fuel number. In this case, 10.8 L/100 km works out to 26 mpg.

Many vehicles now include fuel consumption readouts, both instant and average. I always figure it out by the fuel I pump into the tank whenever I can, but I sometimes only have the computerized number, such as on a single day’s drive on a manufacturer’s launch, when I don’t have the opportunity to use a full tank or to fill the vehicle. In that case, I’ll include it in the story, with an explanation. That said, I’ve sometimes checked a test car’s computerized readout against the “real” numbers I figure out from the fuel used, and have found that the car’s computer is pretty accurate.

The amount of fuel I use in a vehicle is affected by many variables – one of which, I often say, is how much my husband drives the car. Different driving habits can produce considerable differences in fuel consumption, and he admits that I can squeeze much better efficiency out of a vehicle that he can. Even relatively small changes, such as the fact that I take my foot off the throttle marginally sooner than he does when approaching slower traffic, and I accelerate with a gentler touch, add up overall. Ambient temperature, traffic, the type of road, idling time, vehicle speed, the length of the trip, number of passengers and the weight of any cargo can all affect how much fuel I go through in a week.

Fuel figures can also vary across Autos.ca as each writer chalks up individual fuel economy ratings. Living in a relatively flat and temperate part of Ontario, I don’t have to deal with hills as our Vancouver correspondent does, or nastier winters suffered by writers who live further north. The vehicles we drive can also be at various stages of “broken in,” as I’ve driven cars with anywhere from a few hundred to close to 20,000 kilometres on the clock.

Although Canada hasn’t adopted the more real-worldly tests now done south of the border, Natural Resources is gradually building an online fuel consumption calculator that encourages drivers to log in and record their actual fuel consumption on their own vehicles. Once a sufficient database is built up, you’ll be able to look at a specific model and see what kind of real-world figures these cars are racking up.

Of course, just as with the reviews on Autos.ca, there will undoubtedly be all different types of fuel figures, each representative of the driver’s location, vehicle use, the weather, and individual driving habits. In a nutshell, fuel consumption really does come down to YMMV … “your mileage may vary.”