The formula with 2 substituted
US gallons = 2 ÷ 3.785411784 = 0.528
The constant is an exact definition, not a rounded factor: the mile is 1.609344 km, the US gallon is 3.785411784 litres and the imperial gallon is 4.54609 litres. The Litres to Gallons Converter explains where each comes from and gives a longer table.
2 litres is 0.528 US gallons and 0.440 imperial gallons. The imperial gallon is 4.54609 litres against the US gallon's 3.785411784, which is why the two answers differ by a fifth.
What 2 litres means in practice
Two litres is just over half a US gallon, 0.528, and a little under half an imperial gallon, 0.440. It is also the classic engine displacement of a mid-size petrol engine, and most people who search this value are thinking of the engine rather than a jug of fuel.