About the pool volume and tank capacity calculator
Volume is the water's surface area times its depth: length × width × average depth for a rectangular pool with a sloping floor, π × radius² × depth for a round pool or upright tank, and π/4 × length × width × depth for an oval. The result is given in litres, US gallons and cubic metres, and the fill time is the volume divided by the flow rate.
The default 10 × 5 m pool, 1 m deep at one end and 2 m at the other, holds 75,000 L (19,813 US gallons) and takes about 42 hours to fill at 30 L/min. Raising its free chlorine by 2 ppm needs 150 g of available chlorine, which is 1.2 L of 12.5% liquid.
One ppm is 1 mg of available chlorine per litre, and the product amount is that mass divided by its strength. Liquid strength is read as trade percent, grams per 100 mL, so 12.5% liquid carries 125 g per litre.
Questions
How do you calculate pool volume in gallons?
Multiply length × width × average depth in feet to get cubic feet, then multiply by 7.48, the number of US gallons in a cubic foot (1,728 ÷ 231 cubic inches). A 30 × 15 ft pool averaging 5 ft deep holds 2,250 ft³, or 16,831 gallons. For a round pool use π × radius² × depth: 24 ft across and 4 ft deep holds 13,536 gallons.
How many litres of water are in a pool?
Multiply length × width × average depth in metres, then by 1,000, since a cubic metre holds 1,000 litres. A 10 × 5 m pool sloping from 1 m to 2 m has an average depth of 1.5 m, so it holds 75 m³, or 75,000 L. A round pool 5 m across with 1.2 m of water holds π × 2.5² × 1.2 = 23.6 m³, or 23,562 L.
How do you find the volume of an oval pool?
Multiply length × width × depth by π/4, about 0.785, because an ellipse covers π/4 of the rectangle around it. A 30 × 15 ft oval with 4 ft of water holds 1,413.7 ft³, or 10,575 US gallons. The common shortcut of length × width × depth × 5.9 gives 10,620 gallons, because 5.9 rounds up 0.785 × 7.48 = 5.875.
How much chlorine raises a pool by 1 ppm?
One ppm needs 1 mg of available chlorine per litre, so 10,000 US gallons (37,854 L) needs 37.9 g: about 10.2 fl oz of 12.5% liquid, 12.8 fl oz of 10% liquid or 2.1 oz of 65% cal-hypo. The CDC advises keeping free chlorine at 1 ppm or more in pools and 3 ppm or more in hot tubs, with pH between 7.0 and 7.8.
How long does it take to fill a pool with a hose?
Divide the volume by the flow rate. At 30 L/min the default 75,000 L pool takes 2,500 minutes, about 41 h 40 min, and at 9 US gallons a minute a 13,536-gallon round pool takes about 25 hours. To find your own flow rate, time how long the hose takes to fill a bucket of known size and divide the volume by the minutes.
How accurate is the pool volume and tank capacity calculator?
Accuracy depends on your inputs and the method's assumptions. Decimal arithmetic uses 50 significant digits, but estimates, numerical methods and source data can be less precise; the displayed rounding does not remove those limits. It is checked against 5 worked examples whose answers come from independent sources; for example, “10 × 5 m pool, 1 m to 2 m deep, +2 ppm with 12.5% liquid” is checked against Python decimal: 10 × 5 × 1.5 = 75 m³; 75,000 L ÷ 30 L/min = 2,500 min; 2 mg/L × 75,000 L = 150 g ÷ 125 g/L = 1.2 L.
Where does the method come from?
Clean Pool Math — chlorine per 10,000 gal per 1 ppm: 13 fl oz of 10% liquid, 2.1 oz of 65% cal-hypo, 2.4 oz of 56% dichlor; PHTA — Sodium hypochlorite (liquid chlorine) fact sheet; CDC — Operating public pools, hot tubs and splash pads (free chlorine and pH levels).