The basic formula for calculating the volume in gallons of a pond is to use the formula L x W X D x 7.5 where L is the Length in Feet, W is the Width and Feet and D is the Depth in feet. Most ponds are not perfectly squares or circles so when you use the pond volume calculator you should make allowances for variations in depth and shape. Try to use averages when you enter the data and when your pond is irregular shaped with depth variations give up to 20% variation to what this calculator shows.
For Rectangular Pond: Water Volume = length (feet) X width X average depth X 7.5 gallons/cu. foot = GALLONS
For an Oval Pond: Water Volume = 0.8 X ( length (feet) X width X average depth X 7.5 gallons/cu. foot) = GALLONS
P3 Save A Drop Water Meter are a great little tool, simply attach between the faucet and hose and the easy to read meter shows you how much water you’re using. It accurately measures both single watering’s use as well as cumulative water usage to accurately calculate your pond. Accurate to 1/10th of a gallon it’s also great for knowing how much dechlorinator to add when you top off your pond.