Garden Pond Volume Calculator

One cubic foot is 1,728 cubic inches and one US gallon is 231 cubic inches, so 1 cubic foot equals about 7.4805 gallons. Pond shape and actual fill level still affect capacity. Chemical dosing and pump sizing also require product instructions, measured water conditions, head loss, and equipment requirements.

The calculator uses 250 gallons per adult koi as a rough planning allowance, not a universal stocking rule. Adult size, pond shape, filtration, aeration, climate, water quality, and maintenance can require much more capacity. Plan for adult fish and consult an experienced pond professional before stocking.

The calculator uses two pond volumes per hour as a rough stocked-koi planning rate. Actual circulation and filtration depend on fish load, filter design, plumbing loss, head height, aeration, climate, and water-quality targets. Use the pump curve at the real head and follow the filter manufacturer's sizing method.

EPDM rubber (such as Firestone PondGard, 45 mil) is the modern default. It lasts 40 to 50 years, flexes with frost heave, and shapes around boulders and shelves. PVC liner costs about half as much per square foot but cracks after 10 to 15 years of UV exposure, especially at the waterline. Concrete is the most permanent option (50+ years if reinforced and sealed) but cracks during freeze-thaw cycles unless you build it like a swimming pool with rebar and a proper bond beam, which doubles the cost. For most backyard ponds, EPDM is the right balance of price, longevity, and DIY-friendly installation.

The calculator's depth warning is a broad planning signal, not a winter-survival guarantee. Required depth and winter equipment depend on local frost, pond volume, stocking, circulation, aeration, and backup plans. Ask a local pond professional how to overwinter fish in your climate.