In the UK, we have always expressed fuel economy (or 'gas mileage' as Colin Chapman called it in the 1950s) in terms of miles per gallon, while Europeans express it in terms of litres/100 kilometres. Some car adverts you see in the UK give both.
(One is clearly the inverse of the other, ignoring the different units. A good mpg is a big number, a good l/100km is a small number. The quick way to convert from one to the other is to divide 282 by it, so 40 mpg = 7 l/100 km and vice versa. For completeness, 16.8 mpg = 16.8 l/100 km).
Both are inherently flawed. All you really want to know is how much it costs in petrol to drive a certain distance, and they both require one more step than necessary:
UK example - a 40 mpg car doing a 50 mile trip, petrol is £1.20/litre:
- 50 miles divided by 40 mpg = 1.25,
- 1.25 times 4.55 (to get from gallons used to litres used) = 5.7 litres (and I defy you to do that in your head - shortcut is times by 5 and knock off 10%)
- 5.7 litres times £1.20 = £6.83
European example - a 7 l/100 km car doing an 80 km trip, petrol is €1.40/litre:
- 80 km by 100 = 0.8
- multiply 0.8 by 7 = 5.6 litres
- then multiply by €1.40 = €7.84
Far better would be to express it in terms of miles/litre (or km/litre in Europe). 40 mpg = 8.8 miles/litre; 7 l/100km = 14.3 km/litre. That only needs two steps:
UK
- 50 miles divided by 8.8 = 5.7
- 5.7 times £1.20 = £6.83
Europe
- 80 km divided by 14.3 = 5.7
- 5.7 times €1.40 = €7.84.
Just saying.
Debate Magazine
