Pond Volume Calculator
Enter the length, width and average depth of your pond. The calculator gives the volume in gallons and liters, the weight of the water and an estimate of the liner size.
How to use this Pond Volume Calculator
- Choose the pond shape and the unit you measured in.
- Measure the length and width at the widest points. For a round pond enter the diameter twice.
- Measure the depth at several points and enter the average.
- Enter the extra liner you want for the edges on each side.
- Press Calculate for volume, weight and liner size.
How to calculate pond volume
Volume is the surface area times the average depth. One cubic foot holds about 7.48 US gallons.
- Rectangle area = length x width
- Oval area = pi / 4 x length x width
- Volume = area x average depth
- Gallons = cubic feet x 7.48
- Liner = length + 2 x depth + 2 x edge, and width + 2 x depth + 2 x edge
Worked example
A rectangular pond is 10 ft long, 8 ft wide and 2 ft deep on average. The area is 80 sq ft and the volume is 160 cu ft, which is 1,197 gallons, or 4,531 liters. The water weighs about 9,982 lb. A liner for this pond would need to be 10 + 4 + 4 = 18 ft long and 8 + 4 + 4 = 16 ft wide with a 2 ft edge on each side.
For an oval pond with the same length and width the volume is smaller, at 125.7 cu ft, because the shape fills only about 78.5% of the rectangle. Knowing the volume is important for choosing a pump, a filter and the right dose of water treatments. Many pumps are rated in gallons per hour, and a common aim is to turn over the pond volume at least once an hour. Ponds with deep and shallow zones are best split into sections and added up.
Assumptions & limits
- The volume uses an average depth. A pond with shelves or a sloping floor needs an average that is worked out with care.
- The oval formula is an approximation of an ellipse.
- The liner size is a simple box estimate. Real ponds with curves and folds may need more, so check with the liner maker.
- Water weight uses 8.34 lb per US gallon.
- Plants, rocks and fish take up some space, which is not subtracted.
Frequently asked questions
How do I calculate pond volume?
Multiply the surface area by the average depth, then multiply cubic feet by 7.48 for gallons.
How do I find the average depth?
Measure at several points and average them, or split the pond into deep and shallow zones.
How do I size a pond liner?
Add twice the depth and twice the edge allowance to both the length and the width.
Why does pond volume matter?
It sets the size of the pump and filter and the dose of water treatments.
How do I calculate an oval pond?
Use pi / 4 times the length times the width for the area.
How heavy is pond water?
About 8.34 lb per US gallon.
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Last updated: November 2026