Rainfall is measured in inches, and a large storm may drop several inches of rain on an area. To convert inches of rainfall to gallons, it will be necessary to specify the area in which are making the measurement. This article will allow you to calculate the gallons of rainwater which accumulate as a result of an inch of rain falling on a square mile of area. This result can be extended to provide the number of gallons over any area and for any amount of rainfall.

Calculate the number of square inches in a square mile by muliplying 5,280 feet per mile by 12 inches per foot. Multiply this result by itself, which yields an answer of 4,014,489,600 square inches per square mile.

Multiply the previous result by one inch of rainfall. The result is that one inch of rain yields 4,014,489,600 cubic inches of water per square mile.

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Divide the result by 231 cubic inches per gallon, and obtain the result of 17,378,743 gallons per square mile for an inch of rainfall.

Calculate the rainfall over any area by multiplying the result in step three by the number of square miles.you are interested in.

Calculate the result of rainfall of greater than one inch by multiplying the previous result by the number of inches of rainfall received.

#### TL;DR (Too Long; Didn't Read)

The total gallons of water produced by Y inches of rainfall over Z square miles is equal to 17,378,743 x Y inches x Z square miles.