The following table gives the capacity of cisterns for each twelve
inches in depth:
_Diameter._ _Gallons._
25 feet 3671
20 „ 2349
15 „ 1321
14 „ 1150
13 „ 992
12 „ 846
11 „ 710
10 „ 587
9 „ 475
8 „ 376
7 „ 287
6-1/2 „ 247
6 „ 211
5 „ 147
4-1/2 „ 119
4 „ 94
3 „ 53
2-1/2 „ 36
2 „ 23
Supposing it was required to find the weight of the water in any
cistern or tank; it can be ascertained by multiplying the number of
gallons by the weight of one gallon, which is 8-1/3 pounds, 8.333. For
instance, taking the largest cistern in the above table containing 3671
gallons: 3671 × 8.33 = 30579.43 pounds.
The table above gives the capacities of round cisterns or tanks. If the
cistern is rectangular the number of gallons and weight of water are
found by multiplying the dimensions of the cistern to get the cubical
contents. For instance, for a cistern or tank 96 inches long, 72 inches
wide, and 48 inches deep, the formula would be: 96 × 72 × 48 = 331,776
cubic inches.
As a gallon contains 231 cubic inches; 331,776 divided by 231 gives
l,436 gallons, which multiplied by 8.33 will give the weight of water
in the cistern.
For round cisterns or tanks, the rule is: Area of bottom on inside
multiplied by the height, equals cubical capacity. For instance, taking
the last tank or cistern in the table: Area of 24 inches (diameter)
is 452.39, which multiplied by 12 inches (height) gives 5427.6 cubic
inches, and this divided by 231 cubic inches in a gallon gives 23
gallons.
Supposing the tank to be 24 inches deep instead of 12 inches, the
result would be, of course, twice the number of gallons.