About the Pond Volume Calculator
This pond volume calculator estimates how much water a garden pond, koi pond or water feature holds. Choose the shape, enter the length and width (or diameter for a round pond) and the average depth, in feet or meters, and it returns the volume in US gallons, liters, imperial gallons and cubic feet, plus the weight of the water.
Knowing the volume is the first step for almost every pond job: sizing a pump and filter, dosing water treatments and dechlorinator, working out salt for fish treatment, and judging how many fish the pond can support. It is also useful when you plan to fill a new pond and want to know how long the hose will run.
Use the average depth, not the deepest point — if a pond has a shelf at 1 ft and a deep zone at 3 ft, estimate the depth across the whole floor. Irregular, kidney-shaped ponds use the average length and width with an 0.85 shape factor, a common allowance for curved sides; for the most accurate figure, note how many gallons it takes to fill the pond from a metered hose.
With the default inputs, the volume (us gallons) is 898 gal. Change any value above to recalculate instantly.
How to use the pond volume calculator
- 1Pick the shape that best matches your pond.
- 2Choose feet or meters and measure the water surface length and width (or diameter).
- 3Take depth readings in several places and enter the average.
- 4Read the volume in gallons or liters and use it to size pumps and dose treatments.
Formula and method
The surface area depends on the shape: length × width for a rectangle, π × diameter² ÷ 4 for a circle, π × length × width ÷ 4 for an oval, and average length × average width × 0.85 for an irregular pond. Multiplying the area by the average depth gives the volume in cubic feet (or cubic meters when you work in meters).
One cubic foot holds 7.48052 US gallons and one US gallon is 3.78541 liters; an imperial gallon is 4.54609 liters. Water weighs about 8.345 lb per US gallon. Sloped sides and planting shelves reduce the real volume, which is why the average depth matters more than the maximum.
- L, W
- Length and width (or diameter) of the water surface
- D
- Average depth of the pond
- 0.85
- Shape factor for irregular, curved ponds
Worked examples
10 × 6 ft rectangular pond, 2 ft deep
The surface is 10 × 6 = 60 sq ft, and at an average depth of 2 ft the pond holds 120 cubic feet. Multiplying by 7.48052 gives about 898 US gallons, or roughly 3,398 liters, weighing nearly 7,500 lb.
Round pond, 8 ft across and 2 ft deep
A circle 8 ft across has an area of π × 8² ÷ 4 ≈ 50.27 sq ft. At 2 ft deep that is 100.5 cubic feet, or about 752 gallons.
Oval koi pond, 4 × 3 m and 1 m deep
An ellipse 4 m by 3 m covers π × 4 × 3 ÷ 4 ≈ 9.42 m². At an average depth of 1 m it holds about 9.42 m³ — 9,425 liters or roughly 2,490 US gallons.
Frequently asked questions
How do I calculate the gallons in a pond?+
Multiply the surface area in square feet by the average depth in feet to get cubic feet, then multiply by 7.48. A 10 × 6 ft pond that averages 2 ft deep holds 120 cu ft × 7.48 ≈ 898 gallons.
How do I measure the average depth of a pond?+
Take depth readings with a pole at several points — shelves, slopes and the deep zone — and average them. Using only the deepest point overstates the volume, especially in ponds with wide planting shelves or sloping sides.
How do I measure an irregular pond?+
Measure the length at its longest and the width at several points, then use the average width. The 0.85 factor allows for curved edges; for the best figure, note a water meter reading before and after filling.
How many fish can my pond hold?+
A common guideline is about 1 inch of goldfish per 10 gallons, while koi need far more — often around 250 gallons per adult koi with good filtration. Stocking lightly keeps water quality stable.
Why does pond volume matter for treatments?+
Dechlorinators, bacteria products, salt and medications are all dosed per gallon or liter. Overestimating the volume can lead to overdosing, so it is worth measuring carefully or checking against a fill reading.