Litres, US gallons and UK gallons
Pond volume calculator
How many litres is your pond? Multiply the surface area by the depth: a 3 × 2 m pond 0.6 m deep holds 3.6 m³, which is 3,600 litres, 951 US gallons or 792 UK gallons. Pick your pond's shape for sloping sides, shelves or an irregular outline.
Result
Pond volume
3,600 litres
951 US gallons · 792 UK gallons
- Gallons
- 951 US gal · 792 UK gal
- Cubic
- 3.6 m³ · 127.1 cu ft
- Water weight
- 3,600 kg (3.6 tonnes, 7,937 lb)
- Surface area
- 6 m² (64.6 sq ft)
- Average depth
- 60 cm (23.6 in)
- Time to fill
- 5 h at that flow, from empty
Worked out as 3 m × 2 m × 0.6 m
How pond volume is worked out
- Straight sides: rectangle length × width × depth; circle π × radius² × depth; oval π × half-length × half-width × depth.
- Sloping sides: measure the top and the bottom. The prismoidal formula, depth ÷ 6 × (top area + 4 × middle area + bottom area), is exact for evenly sloping sides; the middle is the outline halfway down.
- Shelf all round: the full outline down to the shelf, plus the smaller inner part, shelf width in from each side, down to the bottom. For an oval this is a close approximation.
- Irregular ponds: average length × average width × the average of several depth readings. More readings give a better average.
One cubic metre is 1,000 litres. Gallons use the exact legal definitions: a US gallon is 3.785411784 litres and a UK (imperial) gallon 4.54609 litres, so 1,000 litres is 264.2 US or 220.0 UK gallons. Fresh water weighs very close to 1 kg a litre, so a 3,600-litre pond holds about 3.6 tonnes of water.
The fill time is the volume divided by the flow, from empty. Knowing the volume also helps size a pump and filter, dose treatments and plan how many fish a pond can hold.
Sources
- Wolfram MathWorld, Prismatoid: the prismatoid (prismoidal) formula, volume = h/6 × (A₁ + 4M + A₂).
- NIST, Handbook 44 (2026), Appendix C: 1 US gallon = 231 cubic inches = 3.785 411 784 litres; 1 foot = 0.3048 m exactly.
- Weights and Measures Act 1985, Schedule 1: 1 gallon = 4.54609 cubic decimetres (litres).
- Blagdon, Minipond filter FAQ: pond volume = average length × average width × average depth × 1,000 litres; time how long a bucket takes to fill to measure a flow.
- USGS Water Science School, Water density: 0.99975 g/cm³ at 10 °C and 0.99802 g/cm³ at 21 °C, so “1 kg per litre” is within 0.2%.
Pond volume questions
How do I calculate how many litres my pond holds?
Multiply length × width × average depth in metres, then multiply by 1,000. A 3 × 2 m pond with an average depth of 0.6 m holds 3.6 m³, or 3,600 litres.
How do I measure an irregular pond?
Measure the length and width in a few places and average them, then push a cane in at five or more points, shallow and deep, and average the depths. Multiply the three averages.
How many gallons are in a cubic metre?
About 264.2 US gallons or 220.0 UK gallons, because a US gallon is 3.785411784 litres and a UK gallon 4.54609 litres.
How heavy is the water in a pond?
About 1 kg per litre, or 8.35 lb per US gallon. A 1,000-litre pond holds roughly a tonne of water, which matters for raised ponds and decks.