The cubic millimetre (or cubic millimeter; US spelling) is a unit of volume and is derived from an SI unit with the symbol mm³.
One cubic millimetre is defined as the volume of a cube with sides one millimetre in length. It is the same as a microlitre. It is equal to 0.000000001m³.
There are 1 billion cubic millimetres in a cubic metre.
The liquid gallon is a unit of volume in the US customary unit system and uses the symbol gal.
It is the most common use of the word gallon and is defined as 231 in³. It is made up of 4 quarts where there are 2 pints in a quart and 16 US fluid ounces in a US pint. There are therefore 128 US fluid ounces in a US gallon.
The term gallon is most prevalent when discussing and trading oil and fuel. To ensure consistency, the temperature of the liquid (typically petroleum or alcohol) is understood to be 15.6 °C (60 °F) at the time of measurement.