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. liquid gallon is defined as 231 cubic inches and is equal to 3.785411784 litres or about 0.13368 cubic feet. 1milliliter (ml) = 0.000264172052 US gallons (gal) = 0.0338140227 US fluid ounces (fl. oz.) = 1/1000 L (Liter, the official SI unit of volume).