Weight in kg is litres at 15 °C times density at 15 °C, divided by 1,000. 1,000 litres of diesel of 832 kg/m³ weighs 832 kg. Turn it round to get litres from kilograms.
Mass is litres at 15 °C × density at 15 °C. Use litres at 15 °C, not litres at the tank's temperature.
Why litres at 15 °C
Weight does not change with temperature, but volume does. Density at 15 °C goes with litres at 15 °C. If your litres were measured warm, correct them first with the volume correction factor calculator.
Figures here are for reference. Your oil company’s certified calibration chart, approved instruments and the Marketing Discipline Guidelines always prevail.
Questions
How much does one litre of petrol weigh?
Between 0.720 and 0.775 kg at 15 °C, since BS-VI petrol must be 720 to 775 kg/m³. A typical figure is about 0.745 kg.
How much does one litre of diesel weigh?
Between 0.810 and 0.845 kg at 15 °C for BS-VI diesel. A typical figure is about 0.830 kg.