Calculating pool volume and chlorine demand correctly
From surface area to the right chlorine level
The water volume is the basis for practically every pool maintenance calculation – from chlorine dosing to the fill quantity for your garden hose. For rectangular pools, simply multiply length × width × depth. Round pools are calculated using the circular area (π × radius²) times depth, and oval pools using the elliptical area (π × half the long axis × half the short axis) times depth.
Many in-ground pools don't have a constant depth but a shallow and a deep end. In practice, the average depth is a good approximation: (shallow depth + deep depth) ÷ 2. Above-ground pools (round/oval) generally have a constant depth.
For chlorine dosing, the rule-of-thumb mass balance applies: 1 gram of pure (active) chlorine per 1 m³ of water raises the chlorine level by about 1 mg/l (ppm). Since commercial products contain only part active ingredient (e.g. 56%, 70% or 90% for multi-tabs), the amount of product used must be correspondingly higher: product amount = (target ppm × volume in m³) ÷ (active ingredient content ÷ 100).