Pond Volume Calculator

Pond volume is calculated differently depending on shape. For rectangular ponds: length × width × average depth. For circular ponds: π × radius² × average depth. Irregular ponds are estimated by dividing into sections. Multiply the result in cubic metres by 1,000 to convert to litres. Most garden ponds hold 500–5,000 litres.

Knowing your pond volume is essential for fish stocking (the general rule is 50–75 litres per centimetre of fish), pump sizing (the pump should circulate the full volume at least once every 1–2 hours), filter selection and dosing treatments (algaecides, dechlorinators and fish medications are all dosed per litre).

Enter the pond dimensions and shape. The calculator shows volume in litres and cubic metres, recommended pump flow rate, and stocking capacity. For ponds with shelves or varying depths, use the average depth or calculate each section separately.

How to calculate pond volume. Rectangular pond: length × width × depth (m × m × m) = volume in m³. 1 m³ = 1,000 litres = 220 imperial gallons. Sample 3m × 2m × 0.6m = 3.6 m³ = 3,600 litres. Oval/curved ponds: use average length × average width × depth, then multiply by 0.85 (correction for irregular shape). Add 5-10% if shelves at different depths. Volume drives all subsequent calculations: filter size, pump rate, treatment doses, fish stocking.

UK pond fish stocking rates. Goldfish: 1 inch of fish per 5 gallons (UK Imperial) = 1cm fish per 22 litres. Koi: much more space — 1 inch per 30 gallons (UK) = 1cm per 132 litres. Sample 3,600L pond: 165cm (5.5ft) total goldfish OR 27cm total koi (one young koi). Stock GRADUALLY (10% capacity initial, increase quarterly). Pond ammonia/nitrate accumulates fast — overstocking = fish death within weeks. Add plants — 50% surface coverage minimum reduces algae and oxygenates water.

Pond pumps and filters — sizing. Pump turnover: pump entire pond volume every 2 hours (general). With fish: every 1 hour. Sample 3,600L pond with fish: 3,600 L/hr pump minimum. Pressurised filter (UV): rated to specific pond volume — undersized = green water, fish disease. Oversized filter never harmful. Pumps: All-Pond Solutions, Hozelock, Oase — UK retail £80-£400. Filter media: foam (mechanical), bio media (biological — must be cycled with fish in 4-6 weeks for nitrifying bacteria).

Building a UK pond — basic costs. Liner: heavy duty butyl 0.75mm £8-£12/m². Sample 4m × 3m pond needs ~5m × 4m liner = 20 m² × £10 = £200. Underlay (protect liner from sharp stones): £2-£4/m² = £40-£80. Pump and filter: £200-£600. UV clarifier: £80-£200. Plants: £50-£200. Edging stones/timber: £100-£400. Excavation: DIY 1-2 days, or hire mini-digger £150-£300/day. Total typical UK domestic pond: £500-£1,500 build + £100-£300/year running costs (electricity for pump, food, treatments).

Pond maintenance year-round. Spring: clean filter, restart pump after winter, test water (ammonia 0, nitrite 0, nitrate <40 ppm). Summer: feed fish daily, top up water (evaporation), thin plants. Autumn: net to keep leaves out (critical — decomposing leaves release toxic gases). Winter: keep area ice-free with floating ball/heater; reduce feeding when water drops below 10°C; stop entirely below 5°C (fish digest slowly, food rots). Annual clean: every 3-5 years (more often heavily-stocked). Don't change all water at once — shocks fish.