Should you want the actual formulas so you can work out your own conversions to scientific accuracy, Wikipedia has a very detailed article explaining Conversion of Units that covers all units of measurement.
Pounds and Ounces: Unit of Mass
The Pound (abbr. lb) is a unit of Mass of the British Imperial System. Now superseded by the Metric System, it is still used in combination with the Metric system in these countries: The United States, The United Kingdom,Australia, Canada, New Zealand, The Republic of Ireland, India, Malaysia, Sri Lanka (formerly Ceylon) and the Hong Kong.
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.