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.
There are 3785.4117840007 milliliter in a gallon. 1 Gallon is equal to 3785.4117840007 Milliliter. 1 gal = 3785.4117840007 mL. A gallon is a unit of volume measurement used widely in the US and a few other countries of the world. The US gallon is usually used for measuring volume of liquid or gaseous substances like gasoline, other types of fuel, etc. One US gallon is equal to roughly 3.79 liters, or 231 cubic inches.