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Pond Volume Calculator — How Many Litres Is My Pond?
Calculate pond water volume in litres and gallons, plus recommended pump flow rate, filter size and UV clarifier wattage.
Maximum length
Maximum width
Typical depth across the pond
Avg depth as fraction of max. 0.6 = stepped garden pond; ~0.4 bowl-shaped, ~0.5 uniform slope (rule of thumb)
450 L/W standard, 225 L/W for koi ponds
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How We Calculate This
Our pond volume calculator works out the water capacity of your pond based on its shape and dimensions, then recommends appropriately sized equipment.
Volume formulas by shape
- Rectangular: Length × Width × Depth × 1,000 litres
- Circular: π × Radius² × Depth × 1,000 litres
- Kidney: Length × Width × Depth × 0.75 × 1,000 litres (approximate shape factor)
- Irregular: Length × Width × Depth × 0.65 × 1,000 litres (approximate shape factor)
The kidney and irregular factors are practical rules of thumb (an inscribed ellipse fills about 78% of its bounding rectangle). For the most accurate result on a complex outline, split the pond into regular sections, work out each one and add them together. Our general volume calculatorhandles cuboid and cylinder shapes and converts straight to litres (1 m³ = 1,000 litres).
Average vs maximum depth
If you enter maximum depth, we estimate the average as 60% of the maximum — a rule of thumb that suits a typical stepped garden pond with marginal shelves and a deeper centre. Bowl-shaped ponds are closer to 40% of the maximum and uniformly sloped ponds about 50%; lower the Max Depth Factor in Advanced Options to match your pond’s profile.
Equipment sizing guide
- Pump: Flow rate = pond volume ÷ 1-2 hours (litres/hr) — turn the full volume over once an hour for fish, once every two hours for a lightly stocked pond
- Filter: Rated for at least the full pond volume
- UV clarifier: roughly 1 watt per 450 litres for a standard pond (a common industry rule of thumb)
These equipment figures are practical sizing guidelines from UK pond suppliers, not a formal standard. For koi ponds or heavily stocked fish ponds, double the filter rating and UV wattage. Always check manufacturer specifications for equipment at the required head height.
Frequently Asked Questions
For a rectangular pond: multiply length x width x average depth (all in metres), then multiply by 1,000 to convert to litres. For example, a pond 3m x 2m x 0.5m average depth = 3,000 litres. For a circular pond, use pi x radius² x depth x 1,000. For kidney or irregular ponds there is no exact formula — as a rule of thumb, take the bounding rectangle and multiply by roughly 0.75 for a kidney/oval and 0.65 for a highly irregular outline. For the most accurate result, divide the pond into regular sections and add them together. Use our Pond Liner Calculator to size the liner for your pond.
Use average depth for the most accurate volume calculation. Most garden ponds have shelves and varying depths, so the average is well below the maximum. If you only know the maximum depth, our calculator estimates the average as 60% of the max, which suits a typical stepped garden pond with marginal shelves and a deeper central zone. Bowl-shaped ponds are nearer 40% of the maximum and uniformly sloped ponds about 50% — if your pond fits one of those profiles, lower the Max Depth Factor in Advanced Options accordingly (it adjusts between 0.4 and 0.8).
Your pump should circulate the entire pond volume at least once every two hours, ideally once per hour. For a 3,000 litre pond, choose a pump with a flow rate of 1,500-3,000 litres per hour. For ponds with waterfalls or fountains, increase the pump size to account for head height — most pumps lose flow rate as the height increases.
For a standard garden pond, allow approximately 1 watt of UV clarifier power per 450 litres of water. A 3,000 litre pond needs approximately 7W, so a 9W unit would be appropriate. For fish ponds with higher stocking levels, increase to 1W per 225 litres. UV clarifiers kill green algae to keep water clear.
To convert litres to UK gallons, divide by 4.546. For example, 3,000 litres = 660 UK gallons. Many pond treatment products in the UK are dosed by litres, but some older products use gallons. Note that UK gallons are different from US gallons (1 UK gallon = 4.546 litres; 1 US gallon = 3.785 litres).
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Last updated: February 2026
Verified against UK standards · estimates only, confirm with your supplier.