Determine the shape of the pond. If it has a roughly regular shape, such as a circle, an oval, a square or a rectangle, you will be using standard geometric formulas to determine the surface area. If your pond is irregularly shaped, you will use a different method.
Measure the pond's surface dimensions. If it is square or rectangular, measure the length and the width. If the pond is circular or oval, measure the circumference. A measuring wheel is the best tool for this, but a tape measure may be used instead.
Determine the surface area. The surface area of a square or rectangular pond is its width times its length.
To obtain the surface area of a circular pond, divide its circumference by 6.28 (twice the value of pi). This will give you the radius (distance from the edge to the center). Then, square the radius (multiply it by itself) and multiply the result by 3.14 (pi). The result is your surface area.
For oval ponds, measure the length and width. Divide each by 2, then multiply the answers together. Multiply this result by 3.14 (pi) and you have your surface area.
Measure an irregularly shaped pond by first imagining a rectangle drawn so the entire pond is contained within the rectangle. Measure the dimensions of your imaginary rectangle and draw the rectangle to scale on a piece of graph paper.
Measure the distance from the imaginary rectangle to the actual edge of your pond at several points around the pond's perimeter. Sketch in your pond to scale on the graph paper. The more measurement points you use, the more accurate your final result.
Count the squares inside the sketch of your pond on the graph paper. Multiply the number of squares by the area of each square. Note that the area of each square is whatever measurement each square represents times itself. This gives you the pond's surface area.
Depth and Volume
Determine the depth of the pond by measuring depth in several places and averaging the results.These methods can be used with ponds of any shape. If your pond is shallow, use a measuring tape. If your pond is deeper than six feet, you can measure its depth using a knotted rope. Tie knots every 3 feet on a rope, weight one end of the rope with something that won't float. Get in a boat and drop the rope into the water in the places you are measuring. As the rope descends into the water, count the knots. Multiply the result by three, and you have the depth of your pond at that point, in feet.
Multiply the surface area of your pond by the average depth of your pond. The result is the size of your pond in cubic feet.
Multiply the cubic footage by 7.48 if you need to know the size of your pond in gallons.
Things You Will Need
- Tape measure
- Measuring wheel
- Graph paper
- Boat (for large, deep ponds)
- A pond calculator, such as the one found at www.practical-water-gardens.com/pondvolumes.htm, can eliminate a lot of the arithmetic for you.