Garden Pond Volume & Pump Size Calculator

Garden Pond Guide

Pond Volume Calculation

Rectangular: V = length × width × average depth. Circular: V = π × (diameter/2)² × depth. Oval: V = π × (length/2) × (width/2) × depth × 0.8. Irregular: approximate as rectangle × 0.7. Convert to litres: multiply m³ by 1000. A common garden pond (2.5m × 1.5m × 0.6m average depth): V = 2.5 × 1.5 × 0.6 = 2.25m³ = 2,250 litres. Minimum pond depth: 60cm minimum recommended (prevents freezing completely in UK winters). 90cm+ in coldest areas. Koi ponds: minimum 1.5m deep (1m working depth + marginal

Pump Sizing

The pump should turn over the full pond volume once every 2 hours (for ornamental ponds). Every 1-2 hours for fish ponds. Every hour for heavily stocked koi ponds. Formula: minimum pump LPH = pond volume in litres / 2. For a 2,250 litre pond: 2250/2 = 1,125 LPH minimum. Choose a pump rated at 1,500-2,000 LPH to allow for head loss (pipe height reduces pump output). Filter: the biological filter must process the full pond volume at least once per 2 hours. Under-filtering is the most common cause

Fish Stocking Capacity

General guidelines (excluding filtration allowances): Koi: allow 500-1,000 litres per koi (adult koi can reach 60-90cm). A 2,250 litre pond can hold 2-4 small/medium koi with a good filter. Goldfish: 50 litres per goldfish (adult = 20-30cm). 2,250 litres = up to 45 goldfish. In practice, allow more space for fish health and comfort. Wildlife pond (no fish): far higher biodiversity — frogs, newts, dragonflies, and native aquatic plants cannot coexist easily with koi (which eat frog spawn and vege

Pond Liner Sizing

Liner size: length = pond length + (2 × max depth) + 0.6m overlap. Width = pond width + (2 × max depth) + 0.6m overlap. Example: 2.5m × 1.5m × 0.8m deep pond: liner = (2.5 + 1.6 + 0.6) × (1.5 + 1.6 + 0.6) = 4.7m × 3.7m. Always buy slightly larger — liner cannot be joined easily in the middle of a pond. EPDM rubber liner: most durable (25-50 year lifespan). Flexible and easy to work with. Butyl rubber: professional grade, highly flexible, expensive. PVC liner: budget option — less durable (10-20