[hp2g]

HP2g is using by definition:

The U.S. liquid gallon is legally defined as 231 cubic inches,[1] and is equal to exactly 3.785 411 784 litres (1 L = 10−3 m3) or 0.133 680 555… cubic feet. This is the most common definition of a gallon in the United States. The U.S. fluid ounce is defined as 1/128 of a U.S. gallon.


British thermal unit (BTU or Btu) is a unit of energy used in the power, steam generation, heating and air conditioning industries. In scientific contexts the BTU has largely been replaced by the SI unit of energy, the joule (J), though it may be used as a measure of agricultural energy production (BTU/kg).