The classic way to convey the error that exists in a measurement is a formula that shows the obtained measurement (X) as a sum of a true score plus some error. One version of this formula is: X = T + e. With this formula in mind, obtaining more precise measures depends on reducing error.
  Mega is the prefix meaning one million, therefore there are one million (1,000,000) gallons in a mega gallon.
U.S. gallon measure around 3.785 liters and approximately 231 cubic inches. The Liquid expands and contracts at a specific temperature, so overcoming the expansion and contraction for a gallon we should know how much a gallon will occupy at a specific temperature for the trade purposes it is very important.