How this calculator works
Box volume = length x width x depth. Volume = box volume x shape factor. Liner length/width = pond dimension + (2 x depth) + (2 x edge overlap). Suggested pump flow = pond liters / target turnover hours.
Worked example
A 4 m x 3 m pond averaging 60 cm deep, with a 0.75 shape factor, holds about 5,400 L. Liner size is roughly 5.8 m x 4.8 m, and a 2-hour turnover suggests a pump moving about 2,700 L/h.
Assumptions to check
- Most garden ponds have sloped or irregular sides, so a simple length x width x depth box overstates real capacity - the shape factor scales that down; use 1.0 for a true vertical-sided box pond.
- The liner estimate adds twice the depth plus an edge overlap to each dimension; underlay and pleats at corners are not included.
- Pump sizing is a starting point only - fish stocking, filtration type, waterfalls, and local guidance change the right flow rate.