Free aquarium calculator
Pond Volume Calculator
Work out how much water your garden or koi pond holds in liters and gallons, plus the pump and liner size you need, for rectangular, round, oval or free-form ponds.
Most ponds have shelves, so the average depth is less than the deepest point. Measure in a few places and average them. The deepest point is used to size the liner.
Pond volume
— US gal
Enter the size and average depth to calculate your pond.
Free-form ponds are estimated at 85% of their bounding rectangle. For a precise figure, split the pond into simple shapes and add them up. Liner sizes include 30 cm (1 ft) of overlap on every edge. Pump flow is the real flow at your pond's height, which is lower than the box rating.
How the pond calculator works
Choose your pond's shape, enter its length and width (or diameter for a round pond) and its average depth in meters or feet. The calculator returns the volume in liters, US gallons, UK gallons and cubic meters, the weight of the water, the surface area, the pump flow you need with and without fish, and the size of liner to buy. Your inputs are saved in the page address, so you can bookmark or share the result.
The formula
Volume is surface area × average depth. A rectangular pond is length × width × depth; a round pond is π × radius² × depth; an oval pond is π × half the length × half the width × depth. Free-form and kidney-shaped ponds are estimated as length × width × depth × 0.85, because they fill roughly 85% of the rectangle around them. One cubic meter is 1,000 liters, and one cubic foot is about 7.48 US gallons.
Worked example
A rectangular pond 3 m long and 2 m wide with an average depth of 0.6 m holds 3 × 2 × 0.6 = 3.6 m³, which is 3,600 liters or about 951 US gallons, and the water weighs 3.6 tonnes. For plants alone it needs a pump moving about 1,800 L/h (475 GPH); with fish, about 3,600 L/h (951 GPH). With a deepest point of 0.8 m, the liner needs to be 5.2 × 4.2 m.
Choosing a pond pump
A pond pump should move the whole volume of water through the filter at least once every two hours for a plant pond, and once every hour for a pond with goldfish or koi, which produce much more waste. The flow printed on the box is measured with no hose and no height to lift water against. Once you add tubing, a filter and a waterfall or fountain, the real flow can drop by half, so check the pump's flow chart at your 'head height' (the height from the water surface to the outlet) and size up if in doubt.
Calculating pond liner size
A liner has to cover the floor, run up every side and leave enough at the edge to anchor under paving or soil. The standard formula is: liner length = pond length + 2 × maximum depth + 2 × overlap, and liner width = pond width + 2 × maximum depth + 2 × overlap, using about 30 cm (1 ft) of overlap per edge. Use the deepest point, not the average, so the liner reaches the bottom everywhere. Shelves and curves are covered by the same sheet, which simply folds into place.
Volume, pump and liner for common pond sizes
Typical garden and koi pond sizes worked out with the calculator above. Pump flow is for a pond with fish (one turnover per hour); halve it for a plant-only pond.
| Pond | Average depth | Volume | With fish (every hour) | Liner size |
|---|---|---|---|---|
| Rectangular · 2.0 × 1.0 m | 0.5 m | 1,000 L · 264 US gal | 1,000 L/h · 264 GPH | 3.8 × 2.8 m · 12.5 × 9.2 ft |
| Rectangular · 3.0 × 2.0 m | 0.6 m | 3,600 L · 951 US gal | 3,600 L/h · 951 GPH | 5.2 × 4.2 m · 17.1 × 13.8 ft |
| Rectangular · 4.0 × 3.0 m | 0.8 m | 9,600 L · 2,536 US gal | 9,600 L/h · 2,536 GPH | 6.6 × 5.6 m · 21.7 × 18.4 ft |
| Rectangular · 5.0 × 4.0 m | 1.2 m | 24,000 L · 6,340 US gal | 24,000 L/h · 6,340 GPH | 8.6 × 7.6 m · 28.2 × 24.9 ft |
| Round · Ø 2.0 m | 0.5 m | 1,571 L · 415 US gal | 1,571 L/h · 415 GPH | 3.8 × 3.8 m · 12.5 × 12.5 ft |
| Round · Ø 3.0 m | 0.6 m | 4,241 L · 1,120 US gal | 4,241 L/h · 1,120 GPH | 5.2 × 5.2 m · 17.1 × 17.1 ft |
| Rectangular · 6.0 × 4.0 ft | 1.5 ft | 1,019 L · 269 US gal | 1,019 L/h · 269 GPH | 3.6 × 3.0 m · 12.0 × 10.0 ft |
| Rectangular · 8.0 × 6.0 ft | 2.0 ft | 2,718 L · 718 US gal | 2,718 L/h · 718 GPH | 4.3 × 3.6 m · 14.0 × 12.0 ft |
| Free-form · 10.0 × 8.0 ft | 2.0 ft | 3,851 L · 1,017 US gal | 3,851 L/h · 1,017 GPH | 5.5 × 4.9 m · 18.0 × 16.0 ft |
| Rectangular · 12.0 × 10.0 ft | 3.0 ft | 10,194 L · 2,693 US gal | 10,194 L/h · 2,693 GPH | 6.7 × 6.1 m · 22.0 × 20.0 ft |
Frequently asked questions
- How do I calculate how many liters my pond holds?
- Multiply length × width × average depth in meters to get cubic meters, then multiply by 1,000 for liters. For a round pond use π × radius² × depth. A 3 × 2 m pond that averages 0.6 m deep holds 3,600 liters.
- How do I calculate pond volume in gallons?
- Measure in feet and multiply length × width × average depth to get cubic feet, then multiply by 7.48 for US gallons (or by 6.23 for UK gallons). A 10 × 8 ft pond averaging 2 ft deep is 160 cubic feet, about 1,197 US gallons if rectangular, or about 1,017 gallons if free-form.
- What size pump do I need for my pond?
- Choose a pump that circulates the whole pond at least once every two hours for plants only, and once an hour if you keep fish. A 3,600-liter pond needs about 1,800 L/h without fish and 3,600 L/h with fish, measured at the height the water has to be lifted.
- How big should my pond liner be?
- Add twice the maximum depth plus about 60 cm (2 ft) of overlap to both the length and the width. A 3 × 2 m pond that is 0.8 m at its deepest needs a 5.2 × 4.2 m liner.
- How deep should a koi pond be?
- Koi ponds are usually at least 1–1.2 m (3–4 ft) deep, with a volume of 4,000 liters (about 1,000 gallons) or more, so the fish have stable temperatures and protection from predators. Goldfish ponds can be shallower, around 60–80 cm (2–2.5 ft), but deeper water stays more stable through summer heat and winter cold.