Swimming Pool Volume Calculator

Pool Volume Guide

Why Accurate Volume Matters

Pool chemical doses are calculated per 1,000 litres (or per 1,000 gallons in the US), so an error in your pool volume leads directly to under- or over-dosing — both of which cause water quality and safety problems. Under-dosing chlorine leaves cloudy, algae-prone water that's a swimming hazard and breeding ground for bacteria. Over-dosing wastes chemicals, irritates eyes and skin, damages pool surfaces and equipment over time, and can be dangerous. For pools with sloping bottoms (the typical 'shallow end / deep end' design), use the average depth across the pool, not just the depth at one point — averaging the shallow and deep ends works for simple V-shaped bottoms but doesn't for L-shaped pools with a sudden drop, where you need to calculate the volume in sections. Pool shapes: a rectangular pool with average depth has volume = length × width × average depth × 1,000 (for litres if dimensions in metres). A circular pool: volume = π × radius² × depth × 1,000. An oval pool: volume = π × (length/2) × (width/2) × depth × 1,000. Irregular pools (kidney-shaped, free-form): divide into rectangles and circles or approximate the area by overlay grid method. A worked example: a 10 m × 5 m rectangular pool averaging 1.5 m depth holds 10 × 5 × 1.5 × 1,000 = 75,000 litres — typical for a UK domestic outdoor pool. Don't forget to subtract for the steps, swim-out areas, and any benches that displace water and reduce the actual volume by 2–5%. Most pool owners get their volume wrong by 10–20% on their first calculation, which is enough to cause real chemical balance problems. This calculator handles standard shapes; for complex pools, calculate each section separately and sum.

Fill Time and Water Cost

Filling a swimming pool from a domestic water supply is a meaningful undertaking — both for time and for the water bill that follows. A standard garden hose delivers 15–25 litres per minute under typical UK domestic mains pressure. So a 50,000-litre pool takes 50,000 ÷ 20 = 2,500 minutes ≈ 42 hours of continuous filling — most of two days if filling at a steady rate from one hose. A larger 75,000-litre pool takes 62 hours, around 2.5 days. For practical filling, run two hoses (typically from the garden tap and the kitchen sink tap with an adapter) to halve the time. Water cost matters significantly: at the UK average metered water rate of around £1.80 per cubic metre (£1.80 per 1,000 litres) in mid-2026, a 50,000-litre fill costs £90 in water, plus a similar amount in sewerage charges if metered (some water companies don't charge sewerage on garden water that doesn't go down the drains, but you may need to inform them). Total typical fill cost: £100–200 for a domestic pool, sometimes more depending on the water company's tariff. For larger pools (over 75,000 litres), a tanker delivery from a specialist pool water supplier becomes economical: typically £10–15 per cubic metre delivered, sometimes cheaper than metered domestic water plus the time saved on hose-filling. Check whether your water supplier requires advance notice or special metering arrangements for large fills; some restrict garden water during drought conditions or during heatwaves. The annual top-up volume (replacing water lost to evaporation and splashout) is typically 1–3% of total pool volume per week in summer for outdoor pools — so a 50,000-litre pool may need 500–1,500 litres of top-up per week, modest compared to the initial fill. This calculator gives you accurate volume so you can plan fill time and budget accurately.

Initial Chemical Dosing

When filling or refilling a pool, initial chemical dosing brings the water from raw tap chemistry to safe, swimmable balanced water — and the doses depend critically on accurate volume. For chlorine: dose at 2 g of stabilised chlorine granules per 1,000 litres to achieve an initial 1–3 ppm free chlorine — the safe swimming range. For a 50,000-litre pool, that's 100 g of granules. Unstabilised chlorine (calcium hypochlorite) dosing is similar but uses different chemistry. Maintain a residual 1–3 ppm using a chlorine feeder, salt chlorinator, or daily manual dosing. pH should be 7.2–7.6 — the slightly alkaline range that minimises eye and skin irritation, maximises chlorine effectiveness, and protects pool surfaces; outside this range chlorine becomes less effective and equipment corrodes. Use pH increaser (sodium carbonate) or pH decreaser (sodium bisulphate) as needed; raw tap water in the UK typically reads pH 7.5–8.2, often needing slight reduction. Alkalinity (the buffering capacity for pH) should be 80–120 ppm — keeps pH stable rather than swinging. Calcium hardness should be 200–400 ppm — too low corrodes plaster surfaces; too high causes scale. Cyanuric acid (chlorine stabiliser) at 30–50 ppm for outdoor pools — protects chlorine from UV degradation. Always test the water chemistry before adding any chemicals (digital test strips or a colour-comparator kit), and re-test 6–12 hours after adding chemicals to see the effect before adding more. Common mistake: adding multiple chemicals together. Add one chemical at a time, run the pump for at least 1 hour, then test before adding the next. Pool chemistry isn't difficult, but it's iterative and depends on accurate dosing — which means starting with accurate volume. Always store pool chemicals safely (locked, child-proof, away from heat), and follow manufacturer's instructions. This calculator helps with the volume; pool chemistry kits guide the dosing.

Energy Efficiency Priorities

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