Pond Volume Calculator
Enter your pond dimensions to get the volume in gallons and liters, plus the right pump flow, UV clarifier size, and liner dimensions for that pond. Works for rectangular, oval, round, and freeform ponds.
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US gallons
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liters
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min pump GPH
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UV watts
Suggested liner size: about (includes sides and a 2 ft overlap). Always add underlayment beneath it. Dose any pond salt or treatment to your gallons, never to the deepest point.
Right-sized gear for a -gallon pond
Auto-matched to your volume. Sizes are starting points; see our reviews for specific picks.
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How to Calculate Pond Volume
The volume of a rectangular pond is length times width times average depth. Measure in feet, multiply the three numbers to get cubic feet, then multiply by 7.48 because there are 7.48 US gallons in a cubic foot. To convert to liters, multiply gallons by 3.785. Oval and round ponds use the circle area, which is pi times the two radii, and a freeform or kidney shape multiplies the rectangular figure by about 0.85 to account for the curved edges.
Why Average Depth, Not Maximum
Ponds are rarely a uniform box. They have sloped sides, planting shelves, and a deeper central zone, so using the single deepest measurement will badly overstate your real volume. Take several depth readings and average them, or use roughly two thirds of your maximum depth for a typical bowl shape. Erring slightly low is safer, because it keeps you from overdosing salt or treatments, which is one of the most common ways to harm koi.
Volume Drives Pump, Filter, UV, and Stocking
Once you know your gallons, the rest follows. Your pump should turn the entire pond over at least once per hour, so a 1,000 gallon pond wants a pump moving at least 1,000 gallons per hour, more if it feeds a waterfall. UV clarifiers are sized at roughly 10 watts per 1,000 gallons to control green water. Filtration and safe koi stocking both scale with volume too. That is why this is the first calculator to run, and why the tool above suggests pump flow, UV wattage, and a liner size the moment you enter your dimensions.
Keep going: size the rest of your pond.
Frequently Asked Questions
How do I calculate the volume of a pond in gallons?
For a rectangular pond, multiply length by width by average depth in feet, then multiply by 7.48, since there are 7.48 US gallons in a cubic foot. For example, a 10 by 6 foot pond averaging 2 feet deep is 120 cubic feet, which is about 898 gallons. For oval or round ponds you use the circle area instead, and for an irregular freeform shape you multiply by roughly 0.85 to account for the curves. This calculator does all of that automatically.
Why does pond volume matter so much?
Almost every other decision flows from your gallons. Your pump is sized to turn the whole volume over at least once an hour, your filter and UV clarifier are rated by volume, your safe koi stocking is set by volume, and any treatment or pond salt is dosed by volume. Getting the gallons right, and slightly conservative, is the foundation of a healthy pond, which is why this is the first number to nail down.
Should I measure average depth or maximum depth?
Use the average depth, not the deepest point. Most ponds have sloped sides and shelves, so the deepest spot overstates the real volume. A good estimate is to take a few depth readings across the pond and average them, or use roughly 60 to 70 percent of the maximum depth for a typical bowl-shaped pond. Slightly underestimating volume is safer than overestimating, especially for dosing.
How many gallons does a koi pond need to be?
Most pond keepers recommend a minimum of about 1,000 gallons for koi, with 3 feet or more of depth, and many aim for 1,500 gallons and up. Koi grow large, often 12 to 24 inches or more, and produce a heavy bioload, so they need volume and depth to stay healthy and to overwinter safely. Goldfish and water gardens can be much smaller. See our koi stocking calculator to match fish to your gallons.
How much bigger should the liner be than the pond?
Your liner needs to cover the bottom, both sides, and leave an overlap around the edge to secure it. The rule is liner length equals pond length plus twice the maximum depth plus about 2 feet for overlap, and the same for the width. This calculator estimates that for you, and you should always add underlayment beneath the liner to protect it from roots and stones.
Does a waterfall or stream add to the volume?
A little, but for planning the main thing a waterfall changes is your pump sizing, not your pond volume. The pump has to move enough water to both turn over the pond and feed the waterfall against the height it has to climb. Use the pond volume here for filtration, stocking, and dosing, then use the waterfall pump calculator to size the pump for your spillway width and head height.