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.
The SI derived unit for volume is the cubic meter. 1 cubic meter is equal to 264.172051242 gallons, or 0.001 megaliter. Note that rounding errors may occur, so always check the results. Use this page to learn how to convert between gallons and megaliters.