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Why is the Acre Foot to Gallon conversion factor different?

The difference comes from rounding.

Our courses use the standard equivalent of 1 Cubic Foot = 7.48 Gal, converts 43,560 Cubic Feet to gallons, and rounds to a whole number, giving us:

1 acre-ft = 325,829 gal

 

 

Differences come from rounding in the Cubic Feet to Gallons Equivalent.

Our course says 1 acre-ft = 325,829 gal

The ABC testing conversion sheet says 1 acre-foot = 326,000 gal

CA State Water Board sheet says 1 acre-foot = 325,851 gal

If you google it, you will find many different answers including: 1 acre-foot = 325,851.427 gallons - AND - 1 acre-foot = 325,851.43188913 gallons

The differences are because the Gallons-to-Cubic Feet Conversion is almost always rounded, and the Final Answer is often rounded as well.

Consider this:

  • 1 Cubic Foot = 7.48 Gal

or more exactly...

  • 1 Cubic Foot = 7.48052 Gal

or even more exactly...

  • 1 Cubic Foot = 7.48051948 Gal

If you use 7.48052 gallons per cubic foot you will get 325,851.4512 gallons/acre-foot.

On the other hand, if you use 7.48 gallons per cubic foot instead, you will come up with 325,828.8 gallons/acre-foot.

Depending on your state, the conversion sheet may have 325,829 gallons per acre-foot, 325,851 gallons per acre-foot, and some use 326,000 gallons per acre-foot.
Because of this, it is best to use the information provided and find the best answer for that specific context.