In connection with windmills, rams, etc., which pump to storage tanks, it is often required to estimate the dimensions of tanks to hold certain amounts of water, or to find how many gallons are held by tanks of certain dimensions.

These tanks are generally either rectangular or cylindrical in shape. In either case the cubic contents of the tank in cubic inches, divided by 231, will show the number of gallons which the tank is capable of holding, 231 representing the number of cubic inches in a gallon. If the dimensions of the tank are in feet, the capacity may be found by multiplying the cubic feet of contents of the tank by 7.476, this quantity representing the number of gallons in a cubic foot.

The following rules will give the capacity in gallons of rectangular and cylindrical tanks.

To find the capacity of a rectangular tank: Multiply the internal length, breadth, and depth in feet together, and multiply this result by 7.476. Or multiply together the three interior dimensions in inches and divide the result by 231.

To find the capacity of a cylindrical tank: Multiply the square of half the interior diameter in feet by 3.1416, multiply this result by the depth in feet, and this result by 7.476. Or multiply the square of half the interior diameter in inches by 3.1416, then multiply this result by the depth in inches, and divide this result by 231.

If a tapering cylindrical tank is used, add the large and small diameters together, and find half this amount. This will give the average diameter, and the contents may then be found by the regular rule for cylindrical tanks.

Thus, the capacity of a rectangular tank measuring 4X5X6 ft. will be found in the following manner:

4 X 5 X 6 X 7.476 = 897 gallons, or

(48 X 60 X 72) / 231 =897

The capacity of a cylindrical tank 5 ft. in diameter and 6 ft. deep will be found as follows:

2.5 X 2.5 X 3.1416 X 6 X 7.476 = 881 gallons, or

(30 X 30 X 3.1416 X 72) / 231 = 881

The capacity of a cylindrical tank tapering from 5 ft. in diameter at the bottom to 3 ft. in diameter at the top, and 5 ft. deep, will be found as follows:

(5 + 3) / 2 = 4 ft. = average diameter,

2 X 2 X 3.1416 X 5 X 7.476 = 470 gallons, or

24 X 24 X 3.1416 X 60 / 231 = 470