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Calculating Volume of Ponds - updated |
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Calculating Volume of Ponds
by Ray Jordan - updated January 2010
Pond owners must know the accurate volume in gallons of their ponds. Pond treatments can be fatal to the fish if volume is over estimated and ineffective if under estimated. Knowing the volume of your pond helps in estimating proper stocking levels and amount of aeration and filtration needed.
Water Meter Method:
The most accurate method to determine pond volume is direct water flow measurement using an accurate water meter. Water meters can be purchased that fit on your water hose or you can utilize your city main water meter for the house provided you do not use any water for other purposes while you are filling your pond. Be aware that on average even with a large diameter a ¾ inch garden hose flow is only about 6-18 gallons per minute. So if we take an average of 12 gallons per minute it would take about an hour to flow 720 gallons. If you you estimate your pond to be 5,000 gallons it would take about 7 hours to fill it and you cannot use any water for other purposes while filling. To use this method you need to completely drain your pond. Then record your water meter reading. Fill the pond to normal level. Record the water meter reading. Subtract the ending number on the meter from the beginning number. If your meter reads gallons the difference will the volume of your pond. If the meter reads cubic feet (like most city meters) you will need to multiply that number by 7.48 = gallons.
Tip: if you are using your main city water meter you can run multiple hoses into your pond at the same time to speed up the filling process.
Salt Method: An alternative method to calculate pond volume is accomplished by adding a known weight of salt and testing for salt concentration (salinity) change. This method requires an accurate salt test kit* as follows:
- Test a pond water sample for salt following the instructions of your test kit. Record this concentration in parts per thousand. For our purposes let’s say it is 0.05ppt
- Add 1 pound of salt per estimated 125 gallons of pond volume. Let’s say we believe our pond is 5000 gallons so we add 40 pounds of salt.
- Wait until all salt has dissolved plus two hours.
- Test a pond water sample for the new salt concentration. Let’s say the new concentration is 1.05 ppt giving us an increase of 1.0 ppt
- Calculate the pond volume using this formula:
- ( P / T ) x 120 = V V= po
- nd volume in gallons
- P = pounds of salt added T = actual concentration CHANGE in parts per thousand (or change in % times 10)
Calculation = (37.5/1.0) X 120 = 4500 gallons
*The kit I have used is made by Aquarium Pharmaceuticals and it is labeled “Pond Care Salt Level Test Kit. You fill a test tube to a specified level then add four drops of 1st dropper bottle to sample. Then count the number of drops of the 2nd dropper bottle needed to turn the test solution from clear to purple.
Estimating Volume Method: This method can only be accurate if the pond walls are vertical, bottom is flat, and sides are either rectangular, square, or round in shape. First you calculate the volume in cubic feet then multiply by 7.48 to convert to gallons. Rectangular/Square Formula (feet) = length x width x depth = volume in Cubic Feet X 7.48 = gallonsExample: 16ft X8ftX5ft = 640 cubic feet = 4,787.2 gallons Circular Formula (feet) = (3.14 x radius x radius) x depth = Volume in cubic feet X 7.48 = gallons
Radius = ½ the diameter of the circle (tank)
Example: Let’s calculate a 13 foot diameter circular pond that is 5 feet deep. 3.14 x 6.5 X 6.5 X 5 = 663.3 cubic feet X 7.48 = 4,961.7 gallons |
