# How do I calculate my pond size? – Decorative Ponds & Water Gardens Q & A – Week Ending August 21st

How do I calculate my pond size? Pete – Steele, AL

If someone were to ask you how big your water garden is, how would you respond? Most pond owners have an idea of how many gallons their pond my hold or how many square feet their water feature occupies, but have you ever really measured to see how close your guesstimates comes to the actual numbers?

Knowing how large your pond is down to the square foot or the nearest gallon is not realistic nor is it, by any means, necessary. You will just want to verify that what you “think” is a 15’ x 20’ is not actually 30’ x 40’. People tend to associate size with common everyday items they see around their home. It is not uncommon to hear someone tell us that their pond is about “half of a horse trailer long” or “up to my knees deep”. This may seem like a reasonable answer at the time, but when trying to break down how many gallons are in your pond, or how many square feet of surface area we are dealing with, we, unfortunately, aren’t sure how long your trailer is or how tall you are. =) To keep everyone on the same page and make sure we are all dealing with the same units of measure, we suggest you break out a tape measure and break the pond down into feet and inches.

You may be wondering to yourself why you even need to really know how much water your pond holds or what it matters if you don’t know its surface area. Bacteria products like Nature’s Defense or Liquid Clear are added to the pond based on the number of gallons you are treating. The same holds true with algae killing products like Tetra Algae Control and even Barley Straw Extract. Other products require an estimate of the pond’s surface area for proper application. Aquatic Plant Packages and Pond Netting are examples of such products. Knowing the size of your pond can also help you determine how many fish your pond should typically hold or what size Pond Vacuum is best suited for your particular application.

Now that you know the whys of sizing your pond, let’s get down to business and measure your pond out. The easiest ponds to measure are those that are shaped as simple circles and rectangles, the more irregular the shape, the less accurate our measurements become.

Length x Width x Height

This is the formula used to find the volume of a rectangular shape. It can still be used to get you in the neighborhood if you are measuring a kidney shaped pond, the numbers you get on paper however will be slightly higher than what your pond actually consists of. Measure your pond at its longest point and then its widest point. To demonstrate, lets say the length came to 15 feet and the width 10 feet. You can then measure the depth of the pond. If it is the same depth throughout use this number in our formula. If you have a plant shelf or the depth varies, measure the maximum depth and cut it in half to create an average depth. Let’s say the pond is 4 feet at its deepest but has some shallow areas for plants. We will use half of that depth, 2 feet, for our formula. If you are just looking for surface area, multiply the length and width (15 x 10) to get 150 square feet. If you are looking to find how many gallons the pond holds then multiply the length by width by height (15 x 10 x 2) to get 300 cubic feet. A cubic foot can hold 7.48 gallons of water so to find out how much 300 cubic feet can hold just multiply the two (300 x 7.48) to get 2,244 gallons. If you are also running a waterfall take into account that there is also some water being held in the stream, use the length and width of the stream to calculate a rough volume on it as well. Just like that you now have the volume of your pond.

Easy As Pi

If your pond is round in shape we will use the formula Surface Area = Pi x R² or in other words Surface Area = 3.14 times radius times radius. The radius of your pond is simply half of the distance across. If the pond is a 10 foot circle then the radius is 5 feet. Multiply 3.14 by 5 and then multiply by 5 once more (3.14x5x5) to get 78.5 square feet of surface area. To find your volume you multiply this number by the depth and convert to gallons just like we did with the rectangular pond.

If you want to know exactly how many gallons are in your pond you can use a meter to physically measure the amount of water it takes to fill their pond using a garden hose. If you are constructing a new water garden or pondless waterfall don’t forget to take into account that some of the water from your pond will be held in the stream bed. Give yourself a little wiggle room when digging the basin pond to hold the extra water if you have to shut off the waterfall for any reason.

We have a few helpful Calculators on our site that can help you find your recommended fish capacity, select the proper pump, and if anything, play with your new found pond dimensions.

POND TALK: Now that you have a better understanding of how to measure your pond compare your results with what you originally estimated. Were you close?