Determining the volume of water in your pond is necessary if you intend to stock the pond with fish or use herbicides to kill unwanted pond vegetation. The most involved aspect of calculating pond volume is obtaining the surface area and average depth measurements. You will most likely need a partner to hold the other end of the tape measure you'll be using, and to help propel the canoe or raft you'll need to make depth measurements. Once these measurements have been calculated, they can be easily plugged into the straightforward formula which is used to determine pond water volume.
Measure the length and width of your pond using a tape measure. Since many tape measures don't extend beyond 25 feet in length, you will probably need to make multiple measurements to obtain both the length and width, adding up each to obtain the final length and width. Round off the results to the nearest whole number.
Multiply the length by the width, and divide this result by 43,560 square feet per acre to determine the surface area. For example, 70 feet multiplied by 95 feet equals 6,650 feet. 6,650 feet divided by 43,560 square feet per acre equals 0.153 acres or 1/15 of an acre.
Take at least 15 different depth measurements of your pond from a canoe or raft with a pole or weighted rope that has marked intervals for every foot of length. Take the measurements at consistently spaced distances from each other to account for a wide variety of pond depth discrepancies.
Add all of the depth measurements together and divide by 15, the number of measurements taken. For example, if all of your depth measurements add up to 96, divide 96 by 15 to come up with an average depth of 6.4 feet.
Multiply the surface area of your pond by its average depth to determine the volume of your pond in acre-feet units. Using the previous examples, a surface area of 0.153 acres multiplied by an average depth of 6.4 feet equals a water volume of 0.98 acre-feet. This could also be rounded off to equal 1 acre-foot of water volume.
Measure the outer perimeter of your circular pond in feet. You may need to make multiple measurements with your tape measure, adding them together when you've come full circle to obtain the perimeter measurement.
Multiply this perimeter measurement by itself, and then divide this result by 547,390 to determine the surface area. For example, a circumference of 812 feet multiplied by itself would equal 659,344 feet. Divided by 547,390, the surface area of the circular pond would equal 1.205 acres or 1 1/5 of an acre.
Record 15 different depth measurements of your pond, spaced at consistent intervals from each other, with a pole or weighted rope marked at one foot intervals.
Add the depth measurements together and divide by 15 to determine the average depth. For example, if all of your depth measurements add up to 43, divide 43 by 15 to come up with an average depth of 2.9 feet.
Multiply the surface area by average depth to determine the volume of your pond in acre-feet units. Using the previous examples, a surface area of 1.205 acres multiplied by an average depth of 2.9 feet equals a water volume of 3.49 acre-feet. This could be rounded off to equal 3 1/2 acre-feet of water volume.
If you have an oval-shaped pond, or an otherwise oblong and irregular pond shape, you can determine the water volume by treating the pond as a rectangle. Measure the width and length of the pond at its widest points and draw an imaginary boundary box on graph paper around the irregular pond shape. This rectangular box should just manage to incorporate the entirety of the pond and vaguely approximate its shape. Then use the formula for square and rectangular-shaped ponds.