At some point in time you will need to know how many gallons that your water
garden holds. The following formula will help you figure the gallons
Note: Length, width and depth measured in Feet.

Length x width x depth x 7.5 = gallons

3.14 X (1/2 the diameter x 1 /2 the diameter) x depth x 7.5 = gallons

Length x width x depth x 6.7 = gallons

Think of your pond as shapes: circle plus oval, oval plus square or whatever shapes you may have. Figure the size of each “shape” and add the
total together.
The best way to figure gallons, because most ponds are irregular shapes, is
to time how long it takes to fill a fivegallon bucket. You can then divide the
gallons by 5 and you will know how many gallons of water your hose is putting
out per minute. Then when you fill your pond, time how long it takes to fill it
with water. Take the number of hours it took to fill and divide by 60 to find
out how many minutes it took Multiply this by the number of gallons. For
instance if it took you 30 seconds to fill the 5gallon pail, you know that your
well is putting out 10 gallons per minute. Divide the hours by 60 to find the
gallons per minute. Write this down in a safe spot! This information is vital
should you ever have to "treat" your pond.

My well puts out 15 gallons per minute and it took me 3 hours to
fill my lily tank. (3 hours x 60 minutes =180 minutes) 180 minutes x 15 gallons
per minute = 2700 gallons. Now if I should have to treat this tank I know I have
to figure 2700 gallons of water. 
