Pond Calculators & Tools
Free, practical calculators for keeping a goldfish or koi pond — size the pond, check stocking density, size the filter, work out feeding amounts, plan water changes, and size a pond liner.
Pond Volume Calculator
Work out how many gallons or litres your pond holds from its shape and dimensions — rectangular, round, oval, or an irregular naturalistic shape
Fish Stocking Density Calculator
Check your total fish length against your pond volume to see whether it's comfortably stocked, crowded, or has room for more — separate guidance for goldfish and koi
Filter Turnover (GPH) Calculator
Convert your pond volume and a target turnover time into the pump flow rate, in gallons per hour, your filtration needs to keep up with
Feeding Amount Calculator
Scale a daily feeding amount to your fish's total weight and the water temperature — goldfish and koi eat far less, or not at all, once the water turns cold
Water Change Calculator
Work out exactly how much water to remove and replace for a given percentage change, in gallons and in bucket-loads
Pond Liner Size Calculator
Size the liner sheet you need to buy from your pond's length, width, and depth, with the standard overlap allowance, before you break ground
Pond Size Reference
Compare pond volume against safe goldfish and koi stocking, required filter turnover, and water-change volume in one table, plus feeding by water temperature — every figure computed by the calculators above