Cubic Millimeters
Cubic millimeters are volume units in the metric system. A cubic millimeter is a unit of volume equal to the volume of a cube with sides measuring one millimeter each. It is a very small unit of volume commonly used to measure tiny amounts of liquids or solids. For example, a single drop of water may have a volume of approximately 50 cubic millimeters.
US liquid gallons
A US liquid gallon is a volume measurement used in the United States for liquids such as water, gasoline, and milk. One US liquid gallon is about 3.78541 liters. A standard bathtub is about 80 gallons of water and a car gas tank can hold anywhere between 12 and 20 gallons of gas.