UK gallons
A UK gallon is a unit of volume used in the United Kingdom for measuring liquids such as fuel and water. One UK gallon is about to 4.54609 liters or 0.16054 cubic feet making it substantially larger than the US gallon.
Cubic Millimeters
A cubic millimeter is the volume of a cube 1 millimeter on each side, so 1,000 of them make a cubic centimeter. It is the same as a microliter, and a drop of water is roughly 50 cubic millimeters.