Pond volume calculator — liner size and pump flow rate

For a rectangular pond: volume (litres) = length × width × depth × 1000. For an oval pond use the ellipse formula: π × (length/2) × (width/2) × depth × 1000. For irregular shapes, estimate the surface area in m² and multiply by depth × 1000 × 0.75 (correction for shallower edges). The calculator handles all three shapes automatically.

A rectangular 2×2 m pond at 0.6 m depth holds 2 × 2 × 0.6 × 1000 = 2400 litres. This is the minimum for a stable ecosystem. Deeper ponds (0.8–1.2 m) are more thermally stable and allow fish to overwinter safely.

Liner length = pond length + 2 × depth + 0.6 m overlap. Liner width = pond width + 2 × depth + 0.6 m overlap. For a 2×1.5 m pond, depth 0.6 m: liner = 3.8 × 3.3 m (12.54 m²). The calculator computes this automatically. Always buy 10% extra for folds and joins.

The pump should turn over the entire pond volume at least once per hour. For a 3000 L pond choose a pump rated at minimum 3000 L/h. For fountains and waterfalls you need 1.5–2× more flow. Use the pump mode in the calculator to find the exact flow rate for your desired turnover.

A minimum of 30–40 cm is needed for an ornamental pond without fish (prevents complete freezing in winter). With fish: 60–80 cm for ornamental fish, 80–120 cm for koi carp. Deeper ponds are thermally and biologically more stable.

In Poland, ponds up to 30 m² and 0.5 m deep do not require a permit or notification. Larger ponds require a notification or full building permit. Check with your local planning authority before you start. Requirements vary in other countries.

Liner area = (length + 2×depth + 0.6) × (width + 2×depth + 0.6). For a 2×1.5 m pond, depth 0.6 m: 3.8 × 3.3 = 12.54 m². Add 10% for overlaps. The calculator shows the exact liner dimensions and area.

EPDM (rubber) liner is the top choice — durable (20–30 years), flexible, and fish-safe. PVC liner is cheaper but less durable (10–15 years). Butyl rubber is the most durable but most expensive. Minimum thickness: 0.5 mm; recommended for EPDM: 0.8–1.0 mm.

Measure or estimate the surface area of the irregular shape using a grid or planimeter. Enter this value in m² in the calculator. The volume will be approximate because irregular ponds are usually shallower at the edges — the calculator applies a 0.75 correction factor.

Select the mode: "Volume & liner" — enter the shape, dimensions and depth; the calculator returns the water volume in litres and m³ plus the required liner dimensions. "Pump" mode — enter the pond volume and desired water turnover rate to get the minimum pump flow rate in L/h and L/min.