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M.P.G. long gone...or is it?


You may have noticed that more and more auto advertising in Canada is showing fuel mileage in miles-per-gallon.

But the official unit of volume for measuring gasoline in Canada is the litre. For measuring distance, it’s the kilometre.

Consequently, the unit of measure for fuel consumption is litres per 100 kilometres (L/100 km).

It’s been this way for 30-plus years.

And yet many cars being sold in Canada these days allow the driver, at the flick of a switch, to measure speed in miles-per-hour and mileage in m.p.g.

It’s almost as if the clock is being turned back.

And, as mentioned, it’s largely because newspaper and radio and TV car ads extol the m.p.g. of various vehicles. It wouldn’t be a problem for those who prefer to use the old Imperial units except for two things:

One, whereas the Imperial system is a measure of economy (distance travelled per volume unit of gasoline), the metric measurement is that of consumption (volume of gasoline per unit, or in this case hundred units, of distance travelled) — the inverse of each other.

That complication makes easy conversion in one’s head somewhat difficult.

The formula for converting L/100 km to m.p.g. (Imperial) is m.p.g. = 282.48 divided by (L/100 km).

The second complication is that the U.S. gallon is not the same as the Imperial gallon. One U.S. gallon equals 3.7854 litres, while an Imperial gallon is equivalent to 4.5461 litres.

So not only is the conversion difficult to make, one also has to consider which gallons are being used in any stated fuel-economy figure. It’s all very confusing.

By the way, if you’re trying to equate U.S. advertising figures to L/100, be aware that the U.S. numbers are determined differently so won’t correspond to the Canadian EnerGuide ratings anyway. The measurement procedures are expected to converge by 2015.

“Why not simplify the system by citing Canadian figures in terms of km/L?” some might ask.

It would certainly make conversion between the two systems easier, but that horse is long-since out of the barn.

So the best advice for those who long for the days of m.p.g. is to accept the fact that they are long gone too, and learn to understand L/100 km.

All you really need to know is that lower is better.