How to Calculate Ponds

Measure the approximate width and length of rectangular ponds. Multiply the length by the width to ascertain the surface area. Divide "L" shape ponds into several rectangles. Calculate each rectangle and then combine the results. Right-angled triangular ponds have half the surface area of a rectangle with the same length and width. Record the total surface area.

Measure the depth of the pond using a measuring pole or a graduated rope with a weight on the end. Create a measuring rope or pole by tying strips of ribbon around it at equidistant intervals. Mark the distance from the bottom end of the pole or rope on each ribbon. Lower the rope or pole until it touches the bottom of the pond, and then estimate the depth from the ribbon markers. Take as many depth readings as possible, covering as much of the pond surface as you can. The more measurements you take, and the more effectively you survey the entire pond, the more reliable your results will become.

Add up all the depth readings and divide the total by the number of readings taken. Use the same units of measurement for the depth as you did for the width and length. For example, if the sum of 20 readings came to 100 feet, the average depth is 100/20, or 5 feet. Multiply the surface area by the average depth to find the volume. For example, a pond with a surface area of 30 feet by 50 feet and a depth of 5 feet has a volume of (30 x 50 x 5) feet or 7,500 cubic feet.

Multiply the cubic feet by 7.48051, the number of gallons in one cubic foot, to determine the gallons in the pond. For example, the capacity of a 7,500-cubic-foot pond is 7,500 x 7.48051 gallons, or just over 56,000 gallons.