Convert l/100 km to mpg

Because the two numbers come from different tests. The European value comes from the WLTP cycle, compulsory for every new registration since 1 September 2018; the American value comes from the EPA five-cycle procedure adopted for model year 2008, which adds a cold start at −7 °C, air conditioning and fast, aggressive driving. The EPA also publishes a combined figure weighted 55 per cent city and 45 per cent highway. A car rated 8.1 l/100 km in Europe converts to 29 mpg, yet its American label may read 26: the arithmetic is exact, it is the two test procedures that do not match.

Rarely, and the gap is now measured on board. European regulation 2018/1832 requires a real-world fuel consumption meter, known as OBFCM, on every new car registered since 1 January 2021, and the data is collected at roadworthiness testing. The first analysis published by the Commission puts the average gap at roughly twenty per cent above the WLTP figure, for petrol and diesel alike. An official 5 l/100 km, that is 47.04 mpg, therefore becomes 6 l/100 km on the road, or 39.20 mpg. Convert the figure you measure, never the one in the brochure.

Because air resistance grows with the square of speed, and the power needed to overcome it with the cube. Going from 130 to 110 km/h saves about one litre per hundred kilometres on an ordinary saloon, turning 7 l/100 km, or 33.60 mpg, into 6 l/100 km, or 39.20 mpg. The Netherlands cut its daytime motorway limit from 130 to 100 km/h on 16 March 2020, and the effect on fleet consumption points the same way. In town the picture reverses: weight and stopping dominate, and aerodynamics count for almost nothing.

Yes, by one and a half to two per cent. Ethanol carries about a third less energy per litre than petrol, so a fuel holding ten per cent of it instead of five needs slightly more volume for the same distance. The United Kingdom made E10 its standard 95 octane grade on 1 September 2021; France introduced it in 2009. The gap becomes obvious with E85, twenty-five to thirty per cent more fuel: a car at 7 l/100 km, or 33.60 mpg, moves to 9 l/100 km, or 26.13 mpg. Whether that pays is a question of price per litre, never of the figure on the dashboard.

Because its official figure blends the kilometres driven on electricity with those driven on fuel, in a proportion set by a regulatory utility factor rather than by how you actually drive. Converted, that 1.6 l/100 km reads 147 mpg, a number no driver ever sees at the pump. The European Commission revised those utility factors on 1 January 2025, which raises the declared consumption of these cars sharply without a single mechanical change. A plug-in hybrid that is never plugged in consumes like an ordinary hybrid carrying a battery, six to eight litres per hundred kilometres.