Find the Approximate Number of Gallons Your Pond Will Be

Find the Approximate Number of Gallons Your Pond Will Be

The actual calculation of how many gallons of water your pond will hold is Total Square Feet x 7.5. To get the total square feet you multiply the LENGTH by the WIDTH by the DEPTH. This calculation works extremely well on a square or rectangle pond. In fact, it worked very well for our personal koi pond because it was uniform in depth and was a square. It was 20 ft. by 20 ft. by 5 ft. deep - exactly. The calculation then was 20 (L) x 20 (W) x 5 (D) x 7.5 which gave us 15,000 gallons.

A perfect circle would be Diameter X Diameter X Depth X 6.5.

Most ponds, however, mimic nature and are NOT exact squares, rectangles or circles. So, what do we do to get the total square feet? We either get an AVERAGE LENGTH, an AVERAGE WIDTH and an AVERAGE DEPTH or we break the pond down into more measurable sections.

Project Pond
We will use the average method of calculating the number of gallons in our project pond. The 19 foot width of the pond is at the widest part. The rock shelves take up a total of 3 of those 19 feet. Although you can't tell it by the sketch, the shortest width of the pond is in the curve and it's about 10 feet. Using common sense I am AVERAGING the pond's WIDTH to be about 11 ft. 3 feet of the 22 feet in the length of the pond accounts for the shallow rock shelves and the rest of the length is quite uniform so I will say the AVERAGE LENGTH to be 19 feet. The pond is 4 ft. deep at the deepest and about 3.5 feet at the waterfall so I'm going to say the AVERAGE DEPTH of our project pond is 3.75 ft. deep. To get an approximate size of our project pond in gallons we multiply our average width (11) by our average length (19) by average depth (3.75) - and that gives us our Square Feet of 783.75. There are 7.5 gallons of water in a square foot. Whenever I calculate gallons for a pond that is irregular like our project pond I use 7 gallons per square foot to calculate the amount of gallons in the pond. I can't tell you why but it seems to always be more accurate than when I multiply the square feet by 7.5 when using irregular shapes. We multiply our square feet (783.75) times 7 and that gives us 5486.25 gallons - or about 5500 gallons.

Unless the pond is an exact rectangle or square you'll never be able to get the exact number of gallons until after the pond is built and filled for the first time. You would then mark the water meter and calculate the gallons that went into the pond. With the averaging method we used on our project pond, however, we can get a close approximate for use with sizing the equipment needed.

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