Knowing the volume of your garden pond is important because this figure will determine how many fish the pond can hold, proper fish medication dosages, chemical measurements and proper pump and filter size. If you haven’t already filled your pond with water, calculating the pond volume is easier. Simply use a water meter that you attach to your hose, which will give you an exact measurement of how many gallons of water used to fill the garden pond. Methods of calculating your pond volume after the pond is filled with water will depend on the shape of your garden pond: rectangular, square, circular, oval-shaped or irregularly shaped.
Rectangle or Square Ponds
Measure the length and width of your garden pond in feet and inches with a tape measure. Lay the tape measure along the sides of the pond, flush with the ground.
Measure the depth of the pond. Extend the tape measure until it touches the bottom of the pond at its deepest point.
Multiply the length by the width, by the depth and by 7.5 (length x width x depth x 7.5). The result will give you the number of gallons for the pond’s volume. For example, if your rectangular pond measures 4 feet in length, 3 feet in width and 3 feet deep, your pond volume is 270 gallons (4 x 3 x 3 x 7.5 = 270).
Calculate the diameter of your circle-shaped garden pond. Measure across the widest part of your pond using your tape measure.
Measure the depth of your garden pond. Extend the tape measure in the deepest part of your pond until it touches the bottom.
Multiply the diameter of the pond by the diameter again, by the depth and by 5.9 (diameter x diameter x depth x 5.9). The result is the pond’s volume in gallons. For example, if your circular pond is 4 feet in diameter and 2 feet deep, the pond’s volume is 188.8 gallons (4 x 4 x 2 x 5.9 = 188.8).
Measure across your pond at the widest part of the oval. Then, measure the length of your pond at the longest part of the oval.
Measure the depth of your pond at the deepest part.
Multiply the length of your oval-shaped pond by its width, by its depth and by 6.7 to determine the volume in gallons (length x width x depth x 6.7). For instance, if your oval-shaped pond is 3.5 feet at its longest part, 2.5 feet at its widest part and 2 feet deep, your pond’s volume would be 117.25 gallons (3.5 x 2.5 x 2 x 6.7 = 117.25).
Measure the longest part across your pond in two perpendicular directions. Draw the shape of your pond to scale on graph paper. If you’re using graph paper with smaller grid squares, count each square as 1 inch, or count each square as 1 foot for larger-grid graph paper.
Shade all the squares inside the pond’s outline on the graph paper. Count the total number of squares on your graph paper. Then, count all the shaded squares, taking into account any half- or quarter-shaded squares.
Subtract the number of shaded squares from the total number of squares on the graph paper. The result will give you the pond’s surface area in feet and inches.
Measure the depth of your pond by extending the tape measure down at the deepest part until it touches the bottom.
Multiply the pond’s surface area by the depth and by 7.5 to determine the pond’s volume in gallons (surface area x depth x 7.5). For instance, if you counted the shaded squares on the graph paper and got 9.75 feet and the pond’s depth is 2.5 feet, your pond’s volume would be 182.81 gallons (9.75 x 2.5 x 7.5 = 182.81).