The formula with 1 substituted
US gallons = 1 ÷ 3.785411784 = 0.264
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.
1 litres is 0.264 US gallons and 0.220 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 1 litres means in practice
One litre is 0.264 US gallons or 0.220 imperial gallons, which is the source of the '3.8 litres to a gallon' rule of thumb Americans use and the '4.5 litres to a gallon' one the British use. Both are rounded; the exact figures are 3.785411784 and 4.54609.