The number of liters in 1 kilogram depends on the density of the substance being measured. The liter is a unit of volume, and the kilogram a unit of mass. One kilogram of shaving cream takes up several liters, while 1 kilogram of steel takes up less than a liter.
Liters and kilograms are approximately equivalent when the substance measured has a density of close to 1 kilogram per liter. A common substance with that density is water. Substances that float on water (like oil) are of lower density and have a greater volume for the same mass. Substances that sink, conversely, are of higher density and have less volume.