3 km/L to mi/L — 3 kilometres per litre in miles per litre

One kilometre per litre is 0.62137119 miles per litre.

3 kilometres per litre is 1.864114 miles per litre. The working is 3 km/L → 1.864114 mi/L.

Because the two measures run in opposite directions. Miles per gallon counts distance per unit of fuel; litres per 100 km counts fuel per unit of distance. One is the reciprocal of the other, so you divide rather than multiply.

The Imperial gallon is about 20% larger, so the same car travels further on one of them. A car rated 30 mpg in the US is around 36 mpg in the UK, with nothing about the car having changed.

The first, by a wide margin. Over 10,000 miles the 15-to-20 change saves about 167 gallons; the 30-to-40 change saves about 83. This is exactly the trap the inverse relationship sets, and why litres per 100 km is the easier measure to reason with.