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 encompasses a huge array of calculations.
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 Now superseded by the Metric System, it is still used in combination with the Metric system in these countries: The United States, The United Kingdom,Australia, Canada, New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.
Measuring Fluids: When measuring any fluid that has a similar mass to water, it is often easier and more accurate to weigh the liquid, than it is to measure it by volume. 1 liter of water weighs 1 kilogram (kg). 500 milliliters (ml) of water weighs 500 g (grams), 56ml of water equals 56 grams. Etc.