SRAC Publication No. 103 Southern Regional Aquaculture Center August 1991 Calculating Area and Volume of Ponds and Tanks Michael P. Masser and John W. Jensen* Good fish farm managers must The contractor who built the pond the length of the tape equals total know the area and volume of all should have accurate records on distance. ponds and tanks. Exact measure- pond area. The county field office Pacing uses the average distance ment of area and volume is essen- of the U.S. Department of Agricul- of a person’s pace or stride. To de- tial in order to calculate stocking ture Soil Conservation Service termine your pace length, measure rates and chemical applications. (SCS) assists with the construction a 100-foot distance and pace it, Stocking fish into a pond of uncer- of many ponds and has engineer- counting the number of strides. ing records on many ponds in tain area can result in poor produc- Pace in a comfortable and natural tion, more disease and possibly each county. Also, the county manner. Repeat the procedure sev- death. Chemical treatments can be offices of the SCS and the USDA eral times and get an average dis- Agricultural Stabilization and ineffective if volume/area is un- tance for your stride. derestimated and potentially Conservation Service (ASCS) have lethal if it is overestimated. aerial photos from which pond For example, if it took you 38,39 area can be estimated, and 40 paces to walk a measured Measurements and calculations 100-foot straight line then the aver- described in this publication can Surveying ponds using a transit is age was 39 paces (38 + 39 + 40 ÷ 3). be made in either English or met- the most accurate way to deter- To get the length of your average ric units. All examples are given mine area. Less accurate but ac- pace divide 100 feet by 39 paces in English units. Conversion tables ceptable methods of measuring (100 ft ÷ 39 paces = 2.56 feet per are provided (at the end of this pond area are chaining and pac- pace). Now, whenever you pace a fact sheet) for those who wish to ing. Inaccuracies in these methods distance, simply multiply the num- use metric units. come from mismeasurements and ber of paces by 2.56 to get the dis- measurement over uneven/slop- tance. Calculating area ing terrain. Measurements made Surface area calculation is an es- on flat or level areas are the most The formula for calculating dis- sential first step. Pond stocking accurate. tances from pacing is: rates, liming rates and other impor- Chaining uses a measuring tape or tant management decisions are Distance = Total Number of Paces x other instrument of known length. (feet) Length of Average Pace based on surface area. An error in Stakes are placed at each end of calculating surface area will inevi- the tape. The stakes are used to set It is a good idea to always pace a tably lead to other problems. or locate the starting point for each distance more than once and aver- Measure distances accurately, cal- progressive measurement and to age the number of paces. culate area and double check all maintain an exact count on the calculations. number of times the tape was Square or rectangular You may not need to measure moved. Sight down the stakes to ponds keep the measurement in a pond area yourself. Ponds built in square or rectangu- straight line. The number of times lar shapes are the most easily * Alabama Cooperative Extension Service the tape was moved multiplied by measured. Square and rectangular In this example the area of the rec- (140 + 162 ÷ 2)) square feet or 1.72 areas are determined by multiply- tangular pond is 75,000 square feet acres. ing length by width. Figure 1 illus- or approximately 1.7 acres. Other pond shapes trates some typical shapes and Areas of ponds which are almost sizes of ponds. square or rectangular can be esti- Other formulas are used to calcu- late ponds that are circular and tri- angular. Even if your pond is not 500 an exact shape, it maybe possible to get a reasonable estimate of its area by using one or a combina- 150 tion of these formulas. Circular pond areas are estimated by the formula: Rectangle or Square - Almost Square or Rectangular - 2 opposite sides same length opposite sides approximately Area = 3.14 x radius same length (Radius is one-half the diameter.) For example, a circular pond with a radius of 75 feet has an area of 17,663 square feet (3.14 x75x 75) or 0.4 acres. The radius can be measured di- 250 rectly or the diameter can be di- vided by 2. A measurement of the diameter in several directions will help to determine if the pond is truly circular. 220 Circular Triangular with 90° angle Triangular pond areas are esti- mated by one of two formulas de- pending on whether the triangle has a square or 90° angle for one of its corners. If a 90° angle is pre- sent the formula is: Area = 1/2 x length x width For example, a triangular pond with a length of 250 feet and a Triangular without 90° angle width of 220 feet has an area of 27,500 square feet (250 x 220 ÷ 2) Figure 1. Common pond shapes. Dimensions given are for calculating the area of these or 0.63 acres. It is important to re- shapes as described in the text. member that the longest side (the hypotenuse) is not needed for the Rectangular pond areas are esti- mated by calculating average calculation, instead the two sides mated by the formula: length and width measurements. that touch the 90º angle are used. If we designate the lengths as A Area = length x width and B, and the width as Y and Z If no 90° angle is present and the then the formula for the area is: sides are unequal, the formula is: Area of the rectangular pond in Figure 1 is: Area = A+B X Y+Z 2 2 Area = 500x 150= 75,000 square feet where S = 1/2 (A+B+C) For example, an almost rectangu- To convert from square feet (ft2) and A, B and C are the lengths of the lar pond that is 470 feet on one sides, to acres, divide by 43,560 (from side and 525 feet on the other long Table 1). side, and 140 feet on one end and For example, a triangular pond with’ three sides of 80,90 and 130 Area = 75,000+ 43,560= 1.72 or 1.7 acres 162 feet on the other end, has an area of 75,123 ((470 + 525 ÷ 2) x feet has an area of 3,549.6 square feet (where S = 150; and 2 or 0.08 acres). Irregularly shaped ponds Many ponds in the Southeast are watershed ponds that have been built by damming valleys. These ponds are usually irregular in shape. Check first with your county SCS office for records on your pond, or for aerial photos in the SCS or ASCS office. If no good records exist then a reasonable esti- mate can be made by chaining or pacing off the pond margins and using the following procedures to Figure 3. Figuring volume of a rectangular tank. calculate area. 1, Draw the general shape of the approximate pond area. For ex- applied to water and to calculate pond on paper (graph paper ample, 896 feet x 320 feet = holding or transport densities. works best). 286,720 square feet or 6.58 acres 2. Draw a rectangle on the pond (286,720 ÷ 43,560). Tanks shape that would approximate It is a good idea to repeat this pro- Most tanks used for holding and the area of the pond if some cedure two or three times and transporting fish are rectangular. water was eliminated and compare your results. You may Rectangular volume is calculated placed onto an equal amount of want to average these results if by the formula: land. This will give you a rectan- they differ. gle on which to base the calcula- Volume = length x width x depth tion of area (See Figure 2 below). If a single rectangle does not fit the pond drawing then try to fit some When measuring a tank, take in- 3. Mark the corners of the rectan- combination of rectangles, circles, side measurements of length and gle (from the drawing) on the and/or triangles. If some combina- width and the depth at the appro- ground around the pond and tion seems to fit, then calculate the priate water level. If a standpipe chain or pace its length and areas of the different shapes, and or other type of overflow drain is width. For example, a length of add the corresponding areas to- present then the height to the over- 350 paces and a width of 125 gether to get the total pond area. flow should be the depth measure- paces would be equal to 896 ment. If the bottom of the tank is feet (350 paces x 2.56 feet/pace Calculating volume sloped toward the drain an aver- [pace length, from above]) by age depth measurement should be 320 feet. Volume measurements are needed to calculate the proper concentra- used. To get average depth of the 4. Multiply the length times width tion of most chemicals which are tank take three measurements: at (see example above) to get the the shallow end, in the middle, and at the overflow.