Calculation note
Litres-to-imperial-gallons conversion is still useful when metric volume records meet UK-style gallon language in fuel economy, garden tanks, older manuals, brewing notes, marine records and classroom unit-conversion work. The page names the gallon system first because that single word changes the number.
The litre is the everyday metric volume record
Litres are widely used on containers, tanks, recipes, product labels and metric worksheets. The litre is not the SI coherent volume unit, but it is accepted for practical volume communication and equals one cubic decimetre.
The imperial gallon has a fixed metric value
The UK imperial gallon is defined as exactly 4.54609 litres. That fixed value lets the calculator use a repeatable conversion instead of a rounded kitchen or fuel-economy approximation.
Gallon wording is the main risk
US liquid gallons and imperial gallons are not interchangeable. A report that says only “gallons” can be ambiguous, so this calculator prints the result as imperial gallons and shows the source litres beside it.