# How Many Gallons Of Water Fall Per Inch Of Rain?

## 2 Answers

Anonymous answered
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.
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Anonymous answered
If the width of water saving is about 1 square mile then the amount of water is 17.38 million gallons.

For details and to check out the chart follow the link below:

ga.water.usgs.gov

Also here is a simple but very accurate formula for calculating how much water is coming off.

Example: Area 2000 sq feet, rain = 8 inches

Take the area (2,000 square feet) and multiply it by 8 (amount of rainfall). Take that number and multiply it by 623. Divide that amount by 1000, and you have the amount of runoff in a season.

Thus, a 2,000-square-foot roof, receiving 8 inches of rain per year, will have about 9,710 gallons of runoff. Or, that same area receiving one inch of rain will have 1,246 gallons of runoff.

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