Convert mpg to l/100 km

Because the two numbers are not measured the same way. The American fleet standard, known as CAFE, is computed from the raw results of two laboratory cycles, while the sticker on the window applies a correction derived from five cycles. The gap runs to roughly twenty to twenty-five per cent: a fleet target of 49 mpg, that is 4.80 l/100 km, corresponds to about 36 mpg on the label, or 6.53 l/100 km. The regulatory figure describes no particular car, it describes a fleet average.

Because the test highway is not your motorway. The EPA highway cycle, known as HWFET, runs 10.26 miles at an average speed of 48.3 miles per hour, that is 77.7 km/h, peaks at 60 miles per hour and never stops once. A European motorway is driven at 110 or 130 km/h, where air resistance has doubled. A highway rating of 40 mpg, that is 5.88 l/100 km, therefore says nothing about what the same car will drink at 130.

About fifteen per cent in city driving at −7 °C compared with 25 °C, according to EPA measurements, and up to twenty-four per cent on trips of five or six kilometers, where the engine never reaches its working temperature. A hybrid loses more still, thirty to thirty-four per cent, since both its battery and its engine operate outside their range. Tyre pressure also falls by roughly 1 psi for every 5.5 °C lost. A summer figure of 30 mpg, or 7.84 l/100 km, therefore drops towards 25 mpg, or 9.41 l/100 km.

Because regenerative braking only pays when you stop and start again, exactly where an ordinary engine wastes the most. This is the one common case where the city figure on an American label beats the highway figure: a recent Toyota Prius is rated around 57 mpg in town, that is 4.13 l/100 km, against 56 mpg on the highway, or 4.20. On a conventional petrol car the order is always the other way round, and a higher city number is a reliable sign of a hybrid.

No, and it is the quietest trap on this page. Canada does publish liters per hundred kilometers, but its values come from the EPA five-cycle procedure, adopted for the 2015 model year, weighted 55 per cent city and 45 per cent highway. Europe publishes the same symbol from the WLTP cycle. Two labels both reading l/100 km can therefore describe two different tests, and the Canadian figure is usually the higher one, which also makes it the closer to real driving.

The mpg figure alone will not tell you: you also need the size of the tank. Converted, 30 mpg is 7.84 l/100 km, so a 50 liter tank gives 638 km, or 396 miles. Range is the tank divided by the consumption, which is exactly what the dashboard recomputes as you drive.

It depends which gallon, and the mpg scale misleads because it is inverted: going from 20 to 25 mpg saves more fuel than going from 40 to 45. Converted, 20 mpg is 11.76 l/100 km and 25 is 9.41, a saving of 2.35 liters per hundred kilometers; 40 is 5.88 and 45 is 5.23, a saving of 0.65. In US gallons a good figure starts around 35 mpg, that is 6.72 l/100 km.