Pond volume calculator
How many gallons or litres is your pond? Enter its size in feet or metres — any shape, sloped floor, marginal shelves or dug sloping sides — and get US gallons, UK gallons and litres with the liner, pump, UV and fish stocking to match.
How to calculate pond volume
- Pick the shape. Rectangle, circle and oval for formal ponds; Irregular for natural shapes; With shelves for ponds with planting ledges; Sloped sides for a dug bowl.
- Measure at water level. Use a tape across the water surface, not the outside of the edging. For depth, push a cane to the bottom and measure the wet part.
- Enter shallow and deep points. A floor that slopes is averaged: a pond 2 ft deep at one end and 3 ft at the other averages 2.5 ft.
- Read every unit at once. US gallons, UK gallons, litres and cubic feet or metres, with water weight, liner size, pump flow, UV wattage and fish stocking.
Pond volume formulas
- Rectangle: length × width × average depth.
- Circle: 3.1416 × (diameter ÷ 2)² × average depth.
- Oval (ellipse): 3.1416 × (length ÷ 2) × (width ÷ 2) × average depth — about 79% of the rectangle around it.
- Irregular: length × average of three widths × average of three depths. See how to measure an irregular pond.
- With marginal shelves: the whole surface × shelf depth, plus the deep centre (inside the shelves) × the extra depth below the shelf.
- Sloped sides: depth ÷ 6 × (top area + bottom area + 4 × middle area) — the prismoidal formula, exact for evenly sloping sides.
Feet give cubic feet: × 7.48 = US gallons, × 6.23 = UK gallons, × 28.32 = litres. Metres give cubic metres: × 1,000 = litres. Water weighs 8.34 lb per US gallon, 10 lb per UK gallon, 1 kg per litre.
Common pond sizes
| Pond | Depth | Volume | Liner |
|---|---|---|---|
| 6 × 4 ft | 2.0 ft | 359 US gal (1,359 L) | 12 ft × 10 ft |
| 8 × 6 ft | 2.0 ft | 718 US gal (2,718 L) | 14 ft × 12 ft |
| 10 × 8 ft | 3.0 ft | 1,795 US gal (6,796 L) | 18 ft × 16 ft |
| 12 × 8 ft | 3.0 ft | 2,154 US gal (8,155 L) | 20 ft × 16 ft |
| 15 × 10 ft | 3.0 ft | 3,366 US gal (12,743 L) | 23 ft × 18 ft |
| 20 × 15 ft | 4.0 ft | 8,977 US gal (33,980 L) | 30 ft × 25 ft |
| 2 × 1.5 m | 0.60 m | 476 US gal (1,800 L) | 4.00 m × 3.50 m |
| 3 × 2 m | 0.80 m | 1,268 US gal (4,800 L) | 5.50 m × 4.50 m |
| 4 × 3 m | 1.20 m | 3,804 US gal (14,400 L) | 7.00 m × 6.00 m |
More in the pond size chart, the liner size chart and the pump size chart. Building a pool instead? Use the pool volume calculator.
Questions
How do I calculate pond volume in gallons?
Multiply length × width × average depth in feet to get cubic feet, then multiply by 7.48 for US gallons or 6.23 for UK gallons. For a round pond use 3.1416 × radius² instead of length × width. A 10 × 8 ft pond averaging 2.5 ft deep holds 200 ft³ = 1,496 US gallons.
How do I calculate pond volume in litres?
Measure in metres and multiply length × width × average depth to get cubic metres, then multiply by 1,000. A 3 × 2 m pond averaging 0.7 m deep holds 4.2 m³ = 4,200 litres.
How do I work out the volume of a pond with a sloping floor?
Measure the depth at the shallow and deep ends and average them. For a pond with sloping sides (a bowl), use the top and bottom dimensions: the calculator applies the prismoidal formula, which is exact for evenly sloped sides.
Are UK gallons the same as US gallons?
No. A UK (imperial) gallon is 4.546 litres and a US gallon is 3.785 litres, so a UK gallon is about 20% bigger. UK pumps and treatments are usually labelled in litres or UK gallons, US products in US gallons.
How accurate is a pond volume calculation?
For a formal pond with straight sides, within a few percent. Natural ponds are harder: averaging three widths and three depths usually lands within 10–15%. If you need an exact figure for dosing, read a water meter while you fill the pond.