Litres are a measurement of volume, while tons are a unit of weight, so the answer varies depending on the density of the substance being measured. The denser the substance, the less of it is needed to reach a ton.
It takes, for instance, almost twice as much propane as it does water to make up a ton. There are even differences in density between different types of water. It takes 887.67 litres of sea water to make one U.S. ton and 907.18 litres of pure water to achieve the same weight. The formula for converting volume to weight is: density = mass/volume.