The conversions are very accurate (10 decimal places) and are calculated for all common units of weight measurement.
Imperial pounds ( 0.45359237 kg ) are used by:
United States of America, South Africa, United Kingdom, Eire, India, Canada, Australia and other former British colonies.
A rough guide when you are measuring liquids: 1 ml of water equals 1 gram, 1 litre of water weighs approx 1 kilo - other liquids may differ.
Wikipedia links covering units of mass show/hide