Pond Volume Calculator

Garden pond volume must be calculated accurately to size the pump correctly, determine filtration capacity, calculate chemical treatments, and maintain healthy water conditions for fish and aquatic plants.

Core formulas by pond shape:

Rectangular: Volume (gallons) = Length (ft) × Width (ft) × Depth (ft) × 7.48

Oval: Volume (gallons) = Length (ft) × Width (ft) × Depth (ft) × 5.87 (π/4 × 7.48 ≈ 5.87)

Circular: Volume (gallons) = π × radius² (ft) × Depth (ft) × 7.48

Metric version: Volume (liters) = Length (m) × Width (m) × Depth (m) × 1,000

Pump sizing rule: Your pump should circulate the entire pond volume once per hour (once every 2 hours for ponds without fish). Pump Flow Rate (GPH) = Total Pond Volume (gallons)

Worked example: Oval pond: 8 ft long × 5 ft wide × 2 ft average depth Volume = 8 × 5 × 2 × 5.87 = 469.6 gallons ≈ 470 gallons Recommended pump: at least 470 GPH flow rate For a koi pond, double it for the extra filtration load: 940 GPH

Pond volume reference table:

Depth matters more than the stocking rules admit

Every fish-per-gallon rule ignores depth, and depth is what actually decides whether fish survive. A wide shallow pond can hold 1,500 gallons and still be uninhabitable: under 2 feet the water swings 20°F between a summer afternoon and dawn, it freezes through in a hard winter, and a heron will simply walk in and clear it out. Goldfish want 2 feet, koi want 3 and preferably 4 where winters are cold. The calculator flags this, because volume alone will happily tell you that a paddling pool holds five koi.

Chemical treatment dosing: knowing the volume is what lets you dose algaecides, beneficial bacteria, water conditioners, and fish medications accurately. Under-dose and nothing happens; over-dose and you can kill the fish you were treating. Measure the volume before adding anything.