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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?

18 Responses

  1. Hi
    I am going to build the pond size 12 feet length and 7 feet wide with the depth is 2.5 feet . Total gallons is 1570 gallons
    Please tell me what size of the pond liner will I need ? Please email me.


    • Hi Lynn – I have also emailed this information to you:

      Liner is sold in 5ft increments, so for a 12 x 7 pond 2.5 ft deep you would need a 15 x 20 liner.
      Liner Width = (2.5 X 2) +1 + 12 = 18
      Liner Length = (2.5 X 2) +1 + 7 = 13

  2. How many gallons of water is in a kidney shape pond ten by forty feet,five ft deep is algae killer API safe for dogs in pond.

    • Hi Kelly – A pond that size is roughly 8,000 gallons assuming the average depth is about 2.5 ft and 5ft is the deepest. The pond water will be safe for pets however the dogs would need to stay out of the pond while the treatment is taking place. You would not want the dogs to consume or swim through the concentrated product. It is safe for fish.

  3. What is the size of a pond which occupies 25000 liters of water in feet?

    • Hi Godfrey – This can vary depending on the depth of the pond but roughly a 30 x 30 pond with an average depth of 4 feet.

  4. I have a 9ft by 6ft pond and just under 6ft deep .how many lites or gallons is in my pond please

    • Hi Maria – If your pond is 6 feet deep all the way across, your pond is approximately 2400 gallons. If there are plant shelves or steps built into the pond then that number is probably closer to 1200 gallons.

  5. We would like to build a three-quarter acre kidney shaped pond and are wondering how to calculate the dimensions for layout and how many gallons would be involved in filling. The bottom would be tapered with the maximum depth of 8 feet.
    Thank you very much

    • Hi Don – For the dimensions, you would likely want to calculate 2 circles plus a small rectangle connecting the 2. This will likely get you closest until you can have an aerial mapping done.

      To calculate the surface acres in a circle: (3.14*Radius*Radius)/43,560. To calculate the surface acres for rectangle: (Length*Width)/43,560.

      To calculate gallons, first you’ll need to know how many acre feet you have: Surfaces Acres*Average Depth. Next (for gallons), Acre Feet*325,000=Gallons of Water.

      Let me know if you have additional questions!

  6. Hi, my pond is 9ft long, 6ft wide and 3ft deep, can you tell me how many gallons there is and what type and size filter tank I need please. Much obliged

  7. Hello could you please help me to work out how much water is in my fish pond
    I need to treat my fish as I have had to remove one with white spot

    My pond is
    Length- 6ft 4inch
    Width- 3ft 8inch
    Depth- 2ft 6inch

    Hope you can help
    Thank you

    Yvette x

    • Hi Yvette- I’m going to assume that the depth of the pond is 2′ 6″ at the deepest point and that there are plant shelves. With that said this is how you would calculate your pond volume. 6.5ft(L) x 3.5ft(W) x 1.25ft(Avg D) (average depth=half of your deepest point) x 7.48(gallons in a cubic ft.)= approx. 215 gallons of water. Good luck with treating your fish and lets us know if you have further questions.

  8. Hello pondguy,

    I happened to stop by while searching for pond related information.

    Going back to this topic, I remember a method which a fellow hobbyist in an aquarium club once told me.

    First what he did was to get an IBC (intermediate bulk container) which is about 1 cubic meters.

    Then he filled the IBC until it is full and reuse it again to fill the pond until it reach the desired level. The last unit, he will estimate based on the graduation marking found on the container.

    Well the guy has a relatively small pond and it’s an odd shaped size so he doesn’t mind going through all the trouble filling up one after one container.

    Hope that helps.

    • Sockyee!!!! Dude are you serious? This is a question about ponds not aquariums. There are numerous sites that you can go to online to input the dimensions of your pond and it will calculate it for you. There is no need to determine the size of your pond by the dark ages method. Sorry Sockyee don’t mean to pounce on ya but wow!!!

      • Yes this is very helpful. I have a koi pond that is about 10 years old. Pond appears to be loosing water due to excessive evaporation! Pond is 10 x7 has 6 koi in it at which 3 are at less18 to 20 inches long and the other 3 are just about 12 inches. I have had the largest ones for 9 years they have never spund.

      • Hi Michael – It sounds really early to have excessive evaporation already. If the pond is going down more than 1″ daily, you may have a leak. Here’s an article about finding leaks: How can I find a leak in my pond?

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