Your weight conversion will be given in all commonly used units of mass
If you need the actual formulas so you can make your own calculations to scientific accuracy, Wikipedia has a brilliant article covering Conversion of Units that covers a huge number of formulas for every conceivable unit of measurement.
As a measurement of mass, the Pound (lb) is a unit of Mass / weight in the Imperial system. Although superseded by the Metric System, it's still commonly used in The United Kingdom, USA, Canada, Australia, New Zealand, The Republic of Ireland
To measuring a liquid with a mass similar to water, weigh it! 1 litre of water weighs 1 kg (kilogram). 500 ml (milliliters or milliliters) of water weighs 500g (grams), 56ml of water weighs 56 grams. Etc.