Pond Volume Calculator
Enter the pond's size at the water surface and its depth to get the volume in gallons, acre-feet, liters and cubic feet.
How to use the Pond Volume Calculator
- In Pond shape, choose Rectangle, Circle, Oval (ellipse) or Irregular (I know the surface area).
- Enter the size at the water surface: Length and Width for a rectangle or oval, Diameter for a circle, or Surface area for an irregular pond. Pick feet, yards or meters (or acres, ft², m², ha for the area).
- In Depth method, choose “Deepest depth and side slope” if the pond has straight sloping sides and a flat bottom, or “Average depth” if you have sounded the pond.
- Enter the Depth. For the slope method this is the deepest depth. For the average method it is the mean depth.
- For the slope method, enter the Side slope (horizontal : 1 vertical). A 3:1 slope is 3 ft across for every 1 ft of depth. Use 0 for vertical walls.
- Read Pond volume (US gallons) and Pond volume (acre-feet), then the other units, the surface area and the flat bottom size.
- Open How it was calculated to see each step with your numbers.
The example buttons load samples. Reset restores the defaults, Copy link stores your inputs in the page address, Copy result copies the result lines, and Print / save as PDF prints the inputs and steps with the date.
How do you calculate the volume of a pond?
Multiply the surface area by the average depth. For a pond that is 50 ft across and 5 ft deep on average, the area is π × 25² = 1,963.5 ft², so the volume is 1,963.5 × 5 = 9,817 ft³. Multiply cubic feet by 7.480519 to get US gallons: 9,817 × 7.480519 = 73,438 gallons. The factor comes from 1 ft³ = 1,728 in³ and 1 US gallon = 231 in³.
How many gallons are in an acre-foot?
An acre-foot is the water covering 1 acre to a depth of 1 foot: 43,560 ft³, which is about 325,851 US gallons. Texas A&M AgriLife rounds it to 326,000 gallons. A 2-acre pond with an 8 ft average depth holds 16 acre-feet, or about 5,213,623 gallons. Acre-feet are the unit most extension guides use for stocking and chemical treatment.
How does the side slope change the volume?
A pond with sloping sides is smaller at the bottom than at the surface, so its volume is less than the surface area times the deepest depth. With the slope method, the tool shrinks the pond by slope × depth on each side. A 100 × 60 ft surface, 6 ft deep with 3:1 sides, has a flat bottom of 64 × 24 ft. It then applies the prismoidal formula: depth ÷ 6 × (top + 4 × middle + bottom) = 6 ÷ 6 × (6,000 + 4 × 3,444 + 1,536) = 21,312 ft³, or 159,426 gallons. A box of the same size would hold 36,000 ft³, so the slope matters. The formula is exact for straight sloping sides and a flat bottom.
What if I only know the shape roughly?
Most real ponds are irregular and the bottom is not flat. Texas A&M AgriLife measures the average depth by taking soundings across the pond and dividing the sum by the number of soundings. Use that number with the “Average depth” method and the surface area from a map or measurement. The Missouri Department of Conservation gives a quick estimate of average depth as one third of the maximum depth. Treat that as a rough guess, not a measurement.
Sources
- NIST SP 811 and NIST Handbook 44, Appendix C — US gallon = 231 in³, acre = 43,560 ft², foot = 0.3048 m
- Texas A&M AgriLife Extension, Pond Measurement — acre-feet = surface acres × average depth; average depth from soundings; 1 acre-foot = 43,560 ft³ (326,000 gallons rounded)
- Missouri Department of Conservation, pond area estimator — average depth as about one third of maximum depth
Worked examples
| Input | Result |
|---|---|
| Rectangle 100 ft × 60 ft, 6 ft deep, 3:1 sides | 159,420 gal (0.4893 acre-ft) |
| Circle 50 ft, 5 ft average | 73,440 gal (0.2254 acre-ft) |
| Oval (ellipse) 80 ft × 40 ft, 4 ft average | 75,202 gal (0.2308 acre-ft) |
| Irregular (I know the surface area) 2 acre, 8 ft average | 5.2136 × 10⁶ gal (16 acre-ft) |
| Rectangle 30 m × 20 m, 2 m average | 317,010 gal (0.9729 acre-ft) |
Calculated by the tool above with these values.
Frequently asked questions
Is the calculator free, and is anything I type uploaded?
Yes, it is free. It runs in your browser, needs no sign-up, and nothing you type is uploaded.
Can I use the results in commercial work?
Yes. Results, steps and printouts can be used in any work, including quotes for liners, aeration or treatment, and no attribution is needed. They are estimates, so measure your pond and check the figures before you buy or dose.
How many gallons are in a 1-acre pond?
It depends on the depth. A 1-acre pond with an average depth of 5 feet holds 5 acre-feet, about 1,629,000 gallons. Choose “Irregular”, enter 1 acre and 5 ft average depth to see the exact figure.
What is the volume of a round pond?
Choose Circle and enter the diameter at the water surface. A 50 ft round pond with an average depth of 5 ft holds about 9,817 ft³, or 73,438 gallons.
How many gallons does one inch of rain add to my pond?
The result shows gallons per inch of depth at the surface. For a 100 × 60 ft pond that is about 3,740 gallons per inch, because 6,000 ft² × 1/12 ft × 7.480519 gal/ft³ = 3,740. This ignores runoff from the land around the pond.
Why does the tool refuse my slope and depth?
The sloping sides would meet in the middle before the bottom. For example, a 3:1 slope on a 60 ft wide pond cannot be deeper than 10 ft. The error message shows the largest depth that fits.
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