3 Ways to Calculate Pond Volume

Many times when creating a feature we focus on the pump, the filter, the beauty. We then find ourselves asking questions down the road when problems in the feature arise. If you are new to the world of water or someone with years of experience you should know quickly the volume of your pond is something you must know. Guess work at the volume often proves sufficient enough, but can sometimes prove fatal to our finned little friends.


There are 3 ways to be able to determine the volume of water in the pond; Math, Meter, & Measure.


This is the method most people use and can be fairly reliable as long as the shape and depth of the pond is simple and uniform. With the math method we are simply finding the cubic footage of the pond and multiplying that by 7.48 (commonly rounded to 7.5) to yield gallons. In a rectangular pond with a uniform depth this would be Length x Width x Depth x 7.48=Gallons. Rare is the pond with a perfect geometrical shape and a uniform depth so you can see this ends up being a guesstimate. We can estimate the AVERAGE of each dimension to achieve an estimate of our pond volume. This estimate may be adequate for most needs; choosing a pump, adding beneficial bacteria, etc. But an overdose with an algaecide or a fish medication becomes a serious risk when using an estimated figure and this puts our beloved pond fish at risk. To assist with this method you can use our online calculator.


The meter method is the easiest and most accurate way to determine water volume, but it does take a little forethought. When first filling the pond put a meter on the garden hose to measure the exact number of gallons added. Inexpensive meters like this are commonly available on many garden centers or big box stores. Or if you forgot to pick up a meter, then you can always use your municipality’s street meter. Make note of the number at the start of pond filling and at the end and subtract the difference. You just need to make sure no one else at the residence uses any water during this period.

Some people completely drain and clean their ponds every year or two. If you didn’t get your metered number the first time around, you could get it when refilling a freshly cleaned pond. If you use an outside company to perform this service, you can ask them to do this for you.


This method is the one for the scientist in all of us. To complete the Measure method you will need pond salt and a salinity meter.

Step 1. Use your salinity to meter to measure the salt content existing in the pond currently.

Step 2. Add pond salt. You will want to add 1 pound of salt for every 100 gallons of estimated pond water. Make note of how many pounds were added.

Step 3. Wait at least 2-3 hours for all the salt to be evenly dispersed through the pond.

Step 4. Take a second reading of the salinity with the salinity meter. Make note of the difference in salinity between the first and second reading.

Step 5. Calculate the volume using the following formula. Pounds salt added x 12 / salinity change = volume in gallons.

Example. We will estimate our example pond to be 1800 gallons. When measuring the salinity at the beginning we find a 0.04% salinity. Adding one pound of salt per 100 gallons means we weigh out 18 pounds of salt and add to the pond. After time for the salt to be fully dispersed we take a second salinity reading of .21% salinity. This means we increased the salinity by .17%. This puts our formula at:

18 x 12 / .17 = 1270.59 gallons

In this example we found that we grossly overestimated the pond volume

Whichever method you choose to determine your pond volume, once you have this very important figure please make note of this somewhere safe…just in case your memory isn’t as great as maybe it once was.