It depends on over what area the rain falls. For example, if the rain only fell on 900 ft^2, that would be about 560 gallons. However, if the rain fell over a square mile then it would be about 17.38 million gallons.

What you need to do is calculate the area in square feet, then multiple that by 1/12 ft or .083 ft, which will yield the volume of water for that area in cubic feet (ft^3). Take the volume in cubic feet (ft^3) from the first equation and multiply it by 7.48 gal/ft^3 to arrive at the total number of gallons over the area. The cubic feet (ft^3) in the second equation cancel each other out and all you have left is gallons.

Alternatively, you can calculate the volume in cubic feet, and divide it by .134 ft^3/gal to arrive at the same result.

What you need to do is calculate the area in square feet, then multiple that by 1/12 ft or .083 ft, which will yield the volume of water for that area in cubic feet (ft^3). Take the volume in cubic feet (ft^3) from the first equation and multiply it by 7.48 gal/ft^3 to arrive at the total number of gallons over the area. The cubic feet (ft^3) in the second equation cancel each other out and all you have left is gallons.

Alternatively, you can calculate the volume in cubic feet, and divide it by .134 ft^3/gal to arrive at the same result.