Definitions To Change Units
There are three types of definitions you should know for changing units, English system definitions, metric system definitions, and changeover definitions between the two systems.
There are a small number of English system definitions that you should know by rote. Notice that we take the same approach here with one of the larger unit being stated first and then some number greater than one of the smaller unit. All of these English definitions are exact definitions except for the cubic feet-to-gallons relationship. Take a look at any edition of the Chemical Rubber Company (CRC) Handbook of Physics and Chemistry and you will see the incredible number of non-metric units and amazing amounts of other information.