One US gallon = 231 cubic inches.

How Much Does Rain Weigh?

I was happily watching the BBC's Victorian Farm Christmas show yesterday when I was struck by a statistic used during a discussion relating to hay making.

Heavy rain would damage the crop, but how to quantify that damage; how much does rain water weigh? According to Mr Acton Scott, the owner of the historic farm where the television production takes place, one inch of rain on one acre of land would weigh 100 metric tonnes.

That's the short answer.

Here's the conclusion from a university study in the US (in imperial measures of course):

'Water in the form of precipitation is unevenly distributed. Each inch of rain is relatively heavy. One inch of rain on a square foot of land weighs 5.20 pounds. One inch of rain on one acre of land weighs 113.31 tons.'

113 tons equals 102 tonnes. Now stay with it.

'The purpose of this report is to explain two procedures to determine the weight of one inch of rain on one acre of land.

'The first approach determines the number of cubic inches of water on one acre and the weight in pounds of one cubic inch of water, then uses these values to determine the weight of one inch of rain on one acre. One acre is one rod wide and one-half mile long. A rod is 16.5 feet. A mile is 5280 feet, and a half mile is 2640 feet. The number of square feet in an acre is 16.5 feet times 2640 feet, which equals 43,560 square feet per acre. There are 144 square inches in a square foot. The number of square inches per acre is 43,560 square feet times 144 square inches, which equals 6,272,640 square inches per acre. One inch of rain times 6,272,640 square inches per acre equals 6,272,640 cubic inches of water per acre. One pint of water weighs one pound (1.04316 lbs/pint). One gallon of water weighs 8.3453 pounds. One cubic foot of water contains 7.48052 gallons. The weight of one cubic foot of water is 7.48052 gallons times 8.3453 pounds, which equals62.42718356 pounds of water per cubic foot. One cubic foot contains 1728 cubic inches. The weight of one cubic inch of water is 62.42718356 pounds divided by 1728 cubic inches, which equals 0.036126842 pounds of water per cubic inch. The weight of one inch of rain on one acre of land is 6,272,640 cubic inches of water per acre times 0.036126842 pounds of water per cubic inch, which equals 226,610.6763 pounds of water per acre. There are 2000 pounds in one ton. The weight of water per acre, 226,610.6763 pounds divided by 2000 pounds per ton, equals 113.3053382 tons of water in one inch of rain on one acre of land.

'The second approach determines the number of gallons in one inch of water over one acre and then determines the weight of that number of gallons of water. One cubic foot of water contains 7.48052 gallons. There are 1728 cubic inches in one cubic foot. The number of gallons of water in a cubic inch is 7.48052 gallons divided by 1728 cubic inches, which equals 0.004329005 gallons per cubic inch of water. There are 6,272,640 cubic inches of water on one acre. This value times 0.004329005 gallons per cubic inch equals 27,154.2876 gallons of water per acre. One gallon of water weighs 8.3453 pounds. The weight of water per gallon, 8.3453 pounds, times 27,154.2876 gallons of water per acre equals 226,610.6763 pounds of water per inch of rain on one acre. This value divided by 2000 pounds per ton equals 113.3053382 tons of water per acre.'

Credit to Llewellyn L. Manske PhD, Range Scientist at the Dickinson Research Extension Center of North Dakota State University.

http://www.ag.ndsu.nodak.edu/dickinso/