How many litres are in a pond
Length × width × depth in metres gives cubic metres, and each cubic metre is 1,000 litres. A 3m × 2m pond with an average depth of 0.8m holds 4.8 cubic metres, or 4,800 litres. You need the volume to dose treatments correctly, size a pump and filter, and plan how many fish the pond can carry.
How this is calculated
- Rectangle or irregular: length × width × depth × 1,000 = litres. For an irregular pond, use average measurements.
- Round: 3.14 × radius × radius × depth × 1,000 = litres (the radius is half the diameter).
- Liner: (length + 2 × depth + 1m) by (width + 2 × depth + 1m). The 1m gives 50cm of overlap on each edge, as in Hozelock's guide.
- Pump flow: the full volume once an hour for koi, and once every two hours for other ponds, from Pondkeeper.
- Gallons are UK (imperial) gallons: litres ÷ 4.546.
Worked example
A garden pond is 3m long, 2m wide and 0.8m deep on average.
Volume: 3 × 2 × 0.8 = 4.8m³ = 4,800 litres (about 1,056 gallons). Liner: 3 + 1.6 + 1 = 5.6m long and 2 + 1.6 + 1 = 4.6m wide. A koi pump needs to move about 4,800 litres an hour; for goldfish, 2,400 litres an hour is the minimum.
Choosing a pump
Pump flow ratings drop as the pump lifts water higher. If you have a waterfall, a fountain or a filter above the water line, check the manufacturer's flow figure at that height, not the maximum on the box. Hozelock also suggests a bigger filtration system for shallow or very sunny ponds.