How do I calculate my pond volume in litres?

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-shaped ponds, calculate as a rectangle and multiply by 0.75.

Should I use average depth or maximum depth?

Use average depth for the most accurate volume calculation. Most ponds have shelves and varying depths, so the average depth is typically 50-60% of the maximum depth. If you only know the maximum depth, our calculator estimates the average as 60% of the max, which works well for typical garden ponds with sloping sides and marginal shelves.

What size pond pump do I need?

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.

What size UV clarifier do I need for my pond?

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.

How do I convert litres to gallons for pond treatments?

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).

Pond Volume Calculator — How Many Litres Is My Pond?

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
Irregular: Length × Width × Depth × 0.65 × 1,000 litres

Average vs maximum depth

If you enter maximum depth, we estimate the average depth as 60% of the maximum. This accounts for typical pond profiles with shelves and sloping sides.

Equipment sizing guide

Pump: Flow rate = pond volume ÷ 1-2 hours (litres/hr)
Filter: Rated for at least the full pond volume
UV clarifier: 1 watt per 450 litres (standard pond)

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

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Last updated: February 2026

All calculations are estimates. Verify with your supplier.