Good fish farm managers must know the area and volume of all ponds and tanks. Exact measurement of area and volume is essential in order to calculate stocking rates and chemical applications.
Stocking fish into a pond of uncertain area can result in poor production, more disease and possibly death. Chemical treatments can be ineffective if volume/area is underestimated and potentially lethal if it is overestimated.
Measurements and calculations described in this publication can be made in either English or metric units. All examples are given in English units. Conversion tables are provided (at the end of this fact sheet) for those who wish to use metric units.
Calculating area:
Surface area calculation is an essential first step. Pond stocking rates, liming rates and other important management decisions are based on surface area. An error in calculating surface area will inevitably lead to other problems.
Measure distances accurately, calculate area and double check all calculations.
You may not need to measure pond area yourself.
The contractor who built the pond should have accurate records on pond area. The county field office of the U.S. Department of Agriculture Soil Conservation Service (SCS) assists with the construction of many ponds and has engineering records on many ponds in each county.
Also, the county offices of the SCS and the USDA Agricultural Stabilization and Conservation Service (ASCS) have aerial photos from which pond area can be estimated, Surveying ponds using a transit is the most accurate way to determine area. Less accurate but acceptable methods of measuring pond area are chaining and pacing.
Inaccuracies in these methods come from mismeasurements and measurement over uneven/sloping terrain. Measurements made on flat or level areas are the most accurate. Chaining uses a measuring tape or other instrument of known length.
Stakes are placed at each end of the tape. The stakes are used to set or locate the starting point for each progressive measurement and to maintain an exact count on the number of times the tape was moved. Sight down the stakes to keep the measurement in a straight line.
The number of times the tape was moved multiplied by the length of the tape equals total distance. Pacing uses the average distance of a person’s pace or stride. To determine your pace length, measure a 100-foot distance and pace it, counting the number of strides.
Pace in a comfortable and natural manner. Repeat the procedure several times and get an average distance for your stride. For example, if it took you 38,39 and 40 paces to walk a measured 100-foot straight line then the average was 39 paces (38 + 39 + 40 ÷ 3).
To get the length of your average pace divide 100 feet by 39 paces (100 ft ÷ 39 paces = 2.56 feet per pace). Now, whenever you pace a distance, simply multiply the number of paces by 2.56 to get the distance.
The formula for calculating distances from pacing is:
Distance = Total Number of Paces x (feet) Length of Average Pace
It is a good idea to always pace a distance more than once and average the number of paces.
Square or rectangular ponds:
Ponds built in square or rectangular shapes are the most easily measured. Square and rectangular areas are determined by multiplying length by width. Figure 1 illustrates some typical shapes and sizes of ponds.
Rectangular pond areas are estimated by the formula:
Area = length x width
Area of the rectangular pond in Figure 1 is:
Area = 500x 150= 75,000 square feet
To convert from square feet (ft2 ) to acres, divide by 43,560 (from Table 1).
Area = 75,000+ 43,560= 1.72 or 1.7 acres
In this example the area of the rectangular pond is 75,000 square feet or approximately 1.7 acres. Areas of ponds which are almost square or rectangular can be estimated by calculating average length and width measurements.
If we designate the lengths as A and B, and the width as Y and Z then the formula for the area is:
For example, an almost rectangular pond that is 470 feet on one side and 525 feet on the other long side, and 140 feet on one end and 162 feet on the other end, has an area of 75,123 ((470 + 525 ÷ 2) x (140 + 162 ÷ 2)) square feet or 1.72 acres.
Authors:
Michael P. Masser and John W. Jensen
