Pond Volume Calculator

Work out the surface area for your pond's shape, multiply by the average depth in feet, then multiply by 7.48 gallons per cubic foot. This calculator does that directly for a rectangle, circle or oval, and the one step people get wrong is using the deepest point instead of a genuine average depth, which overstates the true volume.

Surface area times average depth gives cubic feet, and cubic feet times 7.48 gives gallons, the exact conversion between a cubic foot (1,728 cubic inches) and a US gallon (231 cubic inches). The calculator above runs this for rectangle, circle and oval shapes, and estimates an average depth from a max depth reading if you don't have a true average measured yet.

It depends entirely on average depth, since a 1 acre (43,560 square foot) surface at 2 feet average depth holds about 651,900 gallons, while the same acre at 4 feet average depth holds about 1.3 million gallons. Enter your own surface dimensions and average depth above rather than relying on a single acre-to-gallon figure, since depth swings the answer by that much.

The most accurate way is to measure depth at several points across the pond and average them directly, since a pond with sloped sides and plant shelves is rarely a uniform depth. If you only know the deepest point, this calculator can estimate an average using a common pond-builder planning convention of roughly 60% of max depth, though that's a trade estimate rather than a precise measurement, and worth confirming once the pond is dug.

Because it overstates volume, often by 30% or more. A garden pond typically has a shallow marginal shelf around the edge for plants and sloped rather than vertical sides, so most of the pond is shallower than its single deepest zone. Multiplying by max depth treats the whole pond as if it were that deep everywhere, which is why this calculator asks for a genuine average depth instead.

Your pond's surface area in square feet, multiplied by 7.48. A 100 square foot surface gains about 748 gallons for every additional foot of average depth, which is a quick way to see how much a design change in depth affects total volume without recalculating from scratch.

A common pond-keeping guideline is roughly 1 inch of fish per 10 gallons for goldfish and other small ornamental fish, and closer to 1 inch per 20 gallons for koi, which produce more waste and grow much larger. This calculator shows both figures scaled to your pond's actual gallon capacity, though real stocking limits also depend on filtration and aeration, not water volume alone.

Using the roughly 1 inch of fish per 20 gallon koi guideline, a 1,000 gallon pond supports about 50 inches of mature koi, which might be five 10-inch koi or fewer larger ones. Plan around adult koi size, not the size they are as juveniles -- a small koi can reach 18 to 24 inches within a few years, so stocking for their current size regularly leads to overcrowding later.

This calculator doesn't size pumps directly, but the gallon figure it gives is exactly what a pump spec sheet needs: pond pumps and filters are typically sized to turn over the full pond volume once every one to two hours, so a 1,000 gallon pond generally wants a pump rated for roughly 500 to 1,000 gallons per hour.

Gallons, not cubic yards. Unlike gravel, soil or mulch, which are ordered by the cubic yard from a supplier, a pond has no delivery volume to order -- what matters afterward is pump turnover rate, filter capacity and fish stocking, all of which are rated in gallons, so this calculator reports gallons as the headline figure rather than cubic yards.

Approximate it with the closest of rectangle, circle or oval, or break an irregular shape into two or three simpler sections and add their volumes together using the average-depth method for each. A pond's actual shape rarely needs pinpoint precision the way a poured concrete structure does, since planting and rock work around the edge change the effective shape anyway.