Pond volume calculator
Type the shape and size of your pond to find how much water it holds, in litres and UK gallons. You also get the liner size, the pump flow for a fish pond and what the water weighs.
Work out your pond
Measure the water, not the hole. Use a tape for length and width, and a cane pushed to the bottom for depth.
About 3,600 litres
- Volume
- 3,600 litres, 792 UK gallons (951 US gallons, which are smaller)
- Surface and depth
- 6.00 m², 60 cm deep on average
- Liner sheet
- 4.50 m × 3.50 m
Includes 30 cm (15 cm each side) of overlap for the edge. Liners come in set sizes, so take the next size up, such as 4.5 × 3.5 m. Underlay is the same size. - Pump flow
- 3,600 litres an hour, to move all the water through once every hour
The flow on the box is usually with no height to push against. Check the flow at the height you need, and choose a pump that still gives this much there. - Weight of water
- About 3.6 tonnes (3,600 kg)
Moving all the water once every hour or two is a common rule of thumb for ponds with fish, not a fixed law: a pond with many fish may need more. The RHS says a wildlife pond needs no filter, and you may not need a pump at all unless you want a fountain or a cascade. If you fit one, choose a pump with a wildlife guard so tadpoles are not sucked in.
How to use it
Pick the shape nearest your pond and measure the water itself, not the hole round it. For a circle you only need the width across. For an odd shape, measure the length in three or four places and take the average, then do the same for the width, and pick how much of that box the pond fills.
If your pond has shelves (shallow ledges for marginal plants) and a deeper middle, choose Shelves and a deep part. Give each level its depth and roughly how much of the surface sits over it. The link in your address bar keeps your pond, so you can come back to it or send it to someone.
How to read it
Litres and UK gallons are what you need for pond treatments, fish stocking and pumps sold in the UK. US gallons are smaller, so we show them only as a note for products from the US.
The liner size is the sheet you need before it is cut. Liners come in set sizes, so buy the next size up. Underlay, the soft layer that stops stones piercing the liner, is the same size. The pump flow is the flow you need at the height you will pump to, not the bigger number on the front of the box.
How it is worked out
Volume is the surface area times the average depth. With shelves, the average depth is each level's depth weighted by its share of the surface. A cubic metre is 1,000 litres, and a UK gallon is exactly 4.54609 litres, the figure set in the Weights and Measures Act 1985. A US gallon is 3.785411784 litres.
For the liner we follow the usual method: the longest length, plus the deepest depth twice (down one side and up the other), plus an overlap at the edge. The RHS asks for at least 15 cm of overlap all round, so we start at 30 cm in total and you can change it. The shape factors for odd-shaped ponds are our own estimate, so treat that answer as close, not exact.
Moving all the water through the pump once every hour or two is a common rule of thumb for ponds with fish. A pond full of fish may need more. The RHS says a wildlife pond does not need a filter, and you may not need a pump at all unless you want a fountain. It also says every pond should be at least 38 cm deep somewhere, so the tool warns you if yours is shallower. Water weighs about a kilogram a litre, which matters for a raised pond or a pond on a deck.
Plan the rest of the garden
A pond brings in birds as well as frogs: our guide to garden birds in the UK shows who to look out for. If you are planting round it this spring, check the average last frost date near you first.
Garden art prints to go with it
Questions people ask
How do I work out how many litres my pond holds?
Multiply the length by the width by the average depth, all in metres, and times by 1,000. A 3 m by 2 m pond 60 cm deep on average holds 3 × 2 × 0.6 × 1,000 = 3,600 litres. For a circle, use 3.1416 × half the width × half the width for the area.
How many litres are in a UK gallon?
Exactly 4.54609 litres. A US gallon is smaller, about 3.785 litres, so check which one a product means.
What size liner do I need?
Length plus twice the deepest depth plus an overlap, and the same for the width. The RHS asks for at least 15 cm of overlap all round. A 3 m by 2 m pond 75 cm deep needs about 4.8 m by 3.8 m, so you would buy 5 m by 4 m.
Does a wildlife pond need a pump?
Usually not. The RHS says a wildlife pond does not need a filter, and plants keep the water healthy. If you want a fountain, fit a pump with a guard so tadpoles are not sucked in.