UK pumps sell litres. Economy is still quoted in miles per imperial gallon. An imperial gallon is 4.54609 litres. A US gallon is 3.785 litres. The same miles and litres therefore produce a higher UK MPG than a US MPG.
300 miles on 30 litres is about 45.5 UK MPG and about 37.9 US MPG. Mixing the two in a spreadsheet is how fleet reports go wrong when a US lease car joins a UK pool.
Cost per mile
Price is per litre. Cost is litres × price, not gallons × price. The UK MPG and fuel cost calculator keeps the units honest. In CarDiary, choose miles and litres in Settings and consumption is labelled MPG.
