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.
UK Barrels
A UK barrel is 36 imperial gallons (not to be confused with American gallons), about 163.659 liters or 0.163659 cubic meters. It is based on the traditional wine barrel used in the United Kingdom.