A pond volume calculator built for garden pond owners, landscapers and koi keepers. Enter your pond’s dimensions and it instantly returns the volume in litres, UK gallons, US gallons and cubic metres — then a full suite of planning figures: exact liner dimensions, recommended pump flow rate, safe fish stocking levels and representative treatment doses, all based on your specific volume.
The tool handles six pond shapes — rectangular, oval, circular, kidney-shaped, irregular and raised rectangular — using the correct geometric formula for each. Switch between centimetres, inches and feet with a single click; every input converts automatically so you never have to do the unit maths yourself.
How it works
Every shape uses a well-established volume formula applied to the water-holding space, with depth representing the average depth (since most ponds are deeper in the centre than at the margins).
Rectangular pond (including square and raised ponds):
V = L × W × D ÷ 1,000
where L, W and D are in centimetres and V is in litres. 1,000 cm³ = 1 litre.
Oval / elliptical pond:
V = (π ÷ 4) × L × W × D ÷ 1,000
The factor π/4 ≈ 0.785 reflects that an ellipse occupies roughly 78.5% of the bounding rectangle.
Circular pond:
V = π × r² × D ÷ 1,000
where r is the radius (diameter ÷ 2). This is the standard cylinder volume formula.
Kidney / freeform pond:
V = factor × L × W × D ÷ 1,000
A shape factor between 0.6 and 0.85 accounts for the irregular outline. A typical kidney pond uses 0.75; a nearly rectangular shape might use 0.85; a heavily indented shape might drop to 0.60. If in doubt, use 0.70–0.75.
Irregular pond:
Measure (or estimate) the surface area in square metres using a tape measure or garden planning app, then enter the average depth. The calculator converts: V = area(m²) × 10,000 × depth(cm) ÷ 1,000.
Liner sizing
The liner needs to cover the full base and both sides of the pond, plus an overlap laid flat on the surrounding ground (typically 30 cm per side, secured with coping stones).
Liner width = pond width + (2 × depth) + (2 × overlap) Liner length = pond length + (2 × depth) + (2 × overlap)
For a circular pond both dimensions are equal. Adjust the overlap slider in the Liner tab and the figures update live. Always round up to the next available roll width — liner off-cuts are far cheaper than a liner that is 10 cm too short.
Pump sizing
Healthy water quality depends on adequate circulation. The widely cited rule:
- General / wildlife / goldfish pond: recirculate the full volume every 2 hours
- Koi pond: recirculate every 1 hour (ideally twice per hour for a heavily stocked pond)
So a 3,000-litre goldfish pond needs a pump rated at least 1,500 L/h, and a koi pond of the same size needs at least 3,000 L/h. The actual pump you buy should be rated 10–20% above the calculated figure to allow for head height (the vertical lift from pump to filter or waterfall) and filter pressure drop.
Worked example
A kidney-shaped garden pond is 350 cm long, 200 cm wide and averages 60 cm deep, using a shape factor of 0.75:
V = 0.75 × 350 × 200 × 60 ÷ 1,000 = 3,150 litres (693 UK gallons)
Liner (30 cm overlap):
Width = 200 + 2×60 + 2×30 = 380 cm (3.8 m) Length = 350 + 2×60 + 2×30 = 530 cm (5.3 m)
Pump (goldfish pond): 3,150 ÷ 2 = 1,575 L/h minimum
Koi stocking: 3,150 ÷ 500 = 6 adult koi maximum
Dechlorinator for a 20% water change (630 L): 630 ÷ 100 × 5 = 31.5 ml
| Pond type | Volume | Liner (W × L) | Min pump |
|---|---|---|---|
| 200×100×50 cm rect | 1,000 L | 2.6 × 3.6 m | 500 L/h |
| 300×200×60 cm rect | 3,600 L | 3.8 × 4.8 m | 1,800 L/h |
| 250 cm dia × 80 cm deep | 3,927 L | 4.7 × 4.7 m | 1,963 L/h |
| 400×250×70 cm oval | 5,498 L | 4.5 × 6.0 m | 2,749 L/h |
All calculations run in your browser — no pond data is sent to any server.