Use simple mathematics to calculate cistern size.
Learn to calculate the size of a cistern to know its water storage capacity. Cisterns are typically used for collection of rain water for use in watering plants, farm fields, and supplying community residents with water. A cistern has a cylindrical shape with a domed or cone shaped top. The volume of the cylindrical portion of the cistern provides a direct measure of its capacity, and the volume depends on the cylinder's height and radius. The radius measures half the total width of the cistern.
Instructions
1. Measure the height and circumference of the cistern in inches. Be sure to measure the height only to the overflow opening on the cistern, since the water will not rise above that point. Measure the circumference as the total distance around the curved side of the cistern. Assume, for example, the height is 80 inches and the circumference is 200 inches.
2. Divide the circumference by two times the number pi to get the cistern's radius in inches. Use 3.14 for pi. Continuing our example leads to 360 inches divided by 6.28, or a radius of 31.8 inches.
3. Multiply the number pi by the square of the radius times the height to obtain the volume of the cistern in cubic inches. Using the example, multiply 3.14 times 31.8 inches times 80 inches for a volume of 7988.16 cubic inches.
4. Convert the volume to gallons by dividing by 231, because a single gallon equals 231 cubic inches. Completing the example yields 7988.16 cubic inches divided by 231 cubic inches per gallon, or a cistern capacity of 34.58 gallons.
Tags: cubic inches, 7988 cubic, 7988 cubic inches, inches divided, radius inches, times inches