There are a variety of U.S. Customary, British Imperial and metric (SI) units for volume. Why is metric the best choice? Consider: The U.S. has two definitions of the pint and quart called the dry and wet measures. Each has a different size, something most Americans probably don't even realize; The U.S. system has an ounce which refers to a fluid volume, but also an ounce that refers to mass; these are not interchangeable. In general, an ounce of liquid does not weigh an ounce! The British Imperial system of liquid and dry measure uses only one ounce, pint and quart, but these differ from any of the U.S. measures as does the British Imperial gallon, peck and bushel. This document uses only U.S. Customary liquid measures and metric units that are relevant to MSDS's. Many of the items you will find on an MSDS come in both English (U.S. Customary System) and metric (International System or SI or cgs) units. The metric system has been adopted by almost every country except the United States. Even in the U.S., scientists and technical people use the metric system because of its ease of use. MSDS Relevance: Be very careful to note the units when reading numbers on an MSDS. If you ever perform a calculation of any sort, always remember to write the units next to each number in your calculation and make sure that they cancel properly. See also: Area Units, Distance Units, Energy Units, Mass Units, Mole, Pressure Units, Temperature Units