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.
Pounds and Ounces: Unit of Mass
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 Although superseded by the Metric System, it's still commonly used in The United Kingdom, USA, Canada, Australia, New Zealand, The Republic of Ireland
Liquid Measurement: 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.