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How do I know how many gallons are in my pond?| Decorative Ponds & Water Gardens Q & A

Q: How do I know how many gallons are in my pond?

Q: How do I know how many gallons are in my pond?

Jolene – New Rochelle, NY

A: Gallons matter. Knowing how much water your pond holds will help you determine the size of aeration and filtration systems you need. It will also help you properly dose your pond with commonly used pond products and determine how many fish your pond can house.

So how do you calculate this all-important figure? Put on your thinking cap, because we’re revisiting some high school geometry.

Rectangular Ponds

The easiest ponds to measure are those that resemble a rectangle. If you’ll recall from geometry class, you can calculate a rectangle’s volume by multiplying its length by its width by its height, so L x W x H.

First, to get your length and width, measure your pond at its longest point and its widest point. Figuring out its depth is a bit trickier, particularly if you have plant shelves or if the pond has a slope. If it is the same depth throughout, use that number in your 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. For instance, let’s say the pond is four feet at its deepest but has some shallow areas for plants. Use half of that depth, or two feet, for your formula.

So let’s put this in real terms: If your pond is 15 feet long by 10 feet wide by 2 feet deep, your pond’s volume is 300 cubic feet. One cubic foot holds 7.48 gallons of water, so multiply 300 by 7.48 to get your total – which equals 2,244 gallons.

Circular Ponds

If your pond is round or oval, you’ll start by using the formula to find the surface area of a circle – which is Pi x Radius2 , or 3.14 x R x R. The radius of your pond is half the distance across, so if your pond is a 10 foot circle, the radius is 5 feet. Your formula will look like this: 3.14 x 5 x 5 = 78.5.

Next, figure out your pond’s depth, just like we did with the rectangular pond. If it’s 4 feet deep with plant shelves and sloped sides, use 2 feet. Then multiply that number by your surface area: 78.5 x 2 = 157 cubic feet.

Finally, convert that number into gallons. One cubic foot holds 7.48 gallons of water, so 157 x 7.48 = 1,174 gallons.

Irregular Shaped Ponds

The more irregular your pond’s shape, the less accurate your measurement will become – but it’s OK. In most cases, you don’t need to pinpoint its volume to the exact gallon. Use whichever formula best resembles your pond’s shape. For instance, if your pond is kidney shaped, use the rectangle formula and remember that the final figure will be slightly higher.

Playing with the Numbers

With your newfound numbers, head over to The Pond Guy’s® online calculator where you can plug in those figures and see how many boulders you need, how many fish your pond can hold, what pump size you need and more.

Now aren’t you glad you paid attention in geometry class?

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How do I calculate my pond size? – Decorative Ponds & Water Gardens Q & A

How do I calculate my pond size?

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 TetraPond® Algae Control and even Barley 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?

How do I calculate my pond size?

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