You must know the volume of your fish pond to administer water dechlorinator or a pond treatment, and you also need this information when choosing a pump and filter. Experienced pond keepers often install a more than adequate filtration system, so the exact volume of a fish pond is not so important for this purpose. However, if you intend to use a dechlorinator, fish medication or algicide, it is vital that you know the volume of your fish pond. Online pond calculators make the job easy, or you can do the calculation yourself with the appropriate formula.
Measure the length, width and depth of your fish pond in feet, and note the three measurements.
Multiply the three measurements together (length times width times depth) to find your pond's volume in cubic feet.
Multiply this number by 7.5 to calculate the volume in gallons.
Measure the diameter of your round pond at the top and the bottom. These figures may be the same if your pond is a fixed depth, but this volume calculation also works if your pond's diameter is smaller at the bottom.
Take a depth reading at the centre of the pond. Multiply the top diameter by the bottom diameter and multiply this total by the depth.
Multiply the total by 0.785 for your pond's volume in gallons.
Fill the 10-gallon bucket with water from the hosepipe, and use the stopwatch to monitor how long this takes.
Restart the stopwatch and place the hosepipe into the empty pond, without stopping or changing the water flow, and monitor the length of time required for the pond to fill up.
Divide the time taken to fill the pond by the time taken to fill the 10-gallon bucket. Multiply the answer by 10 for your fish pond's volume in gallons.
The hosepipe method provides the most accurate result and is useful for large, irregular ponds. It can be inconvenient because the pond must be completely empty before you start your calculation.