Pond Calculator
Estimate water capacity for a rectangular pond from its internal dimensions.
How the result changes
Only water length changes; all other inputs stay at your current values. The line illustrates the formula across the shown range. This is not a forecast of real-world outcomes.
About this calculation
A pond's advertised outer footprint can be very different from the water it actually holds. This calculator uses inside water dimensions and average depth to estimate the fill volume in cubic feet, US gallons, and litres. Calculate pond when sizing a tank or vessel.
Formula
cubic feet = inside length × inside width × average water depth
Worked example
With Water length: 12 ft, Water width: 8 ft, Average water depth: 2 ft, water volume is 192 ft³.
Inputs and units
Measure the wet length and width at the operating water level. Enter an average depth that represents the water-filled volume: for a stepped pond, estimate each zone's cubic feet separately and sum them rather than using the deepest spot throughout.
- Water length (ft): Measure the inside length at the water line for a rectangular pond.
- Water width (ft): Use inside water width rather than the outer dimensions of edging.
- Average water depth (ft): Average shallow and deep zones by their volume, not simply their maximum depth.
Calculation and worked example
Multiply the three internal dimensions to obtain cubic feet. Each cubic foot equals approximately 7.48052 US gallons or 28.31685 litres, so the two liquid units are direct conversions of the same geometric volume In compact notation, cubic feet = inside length × inside width × average water depth.
A rectangular water space 12 ft long, 8 ft wide, and 2 ft deep holds 192 ft³. That is approximately 1,436.26 US gallons or 5,436.83 litres at the stated dimensions.
How to use the answer
Treat the volume as a capacity estimate at the chosen water level. A liner folded at corners, stones, plant shelves, and a sloped floor reduce actual water compared with a full rectangular box of outer dimensions.
The gallons number helps compare pump and filter specifications written in US units, while litres fit metric treatment labels. If a product requires an exact dosage, measure actual filled water or follow its instructions rather than assuming the box estimate is exact.
Assumptions and checks
The model is a rectangular prism and assumes one representative depth. It does not calculate evaporation, rainfall, circulation, or water displaced by gravel, shelves, equipment, or decorations.
Do not mix imperial and US gallons; this page reports US gallons. Measuring depth to the bottom of an empty excavation when the pond will be filled below the rim will overstate the stored water.
A 1 ft cube is 1 ft³ and holds about 7.48 US gallons. Compare your pond with a set of such cubes, then check that litres are about 3.785 times the US-gallon result.
Common questions
What does the water volume result represent?
It is the water-filled rectangular volume from the entered internal dimensions, expressed first in cubic feet and then in two liquid-capacity units.
What should I check before relying on this result?
Check the water line, shelves, sloped sides, and displacement by stones. For dosing, confirm actual filled capacity when precision matters.
Inputs
- Water length (ft)
- Water width (ft)
- Average water depth (ft)