Every pool chemistry dose, pump sizing, heater sizing and water bill starts from one number: how much water the pool holds. Pool volume is easy to get wrong because most pools slope from a shallow end to a deep end, and because gallons and litres get mixed up. This calculator uses the average depth and the standard shape formulas, then applies the volume to the questions people actually have.
How it is calculated
- Average depth = (shallow end + deep end) ÷ 2. This is accurate for a steady slope, which most pools have.
- Rectangle: length × width × average depth. Round: π × (diameter ÷ 2)² × depth. Oval: π × ½ length × ½ width × depth. Kidney or freeform: length × width × depth × 0.85, the usual correction for the curved shape.
- Cubic feet × 7.48 = US gallons; × 3.785 = litres.
Example
A 32 × 16 ft rectangular pool, 3.5 ft in the shallow end and 8 ft in the deep end: average depth 5.75 ft, volume 2,944 ft³, about 22,000 gallons or 83,000 litres. That is 83 tonnes of water, roughly 40 hours from a garden hose, and needs a pump moving about 46 gallons a minute to turn the water over in 8 hours. To raise free chlorine by 1 ppm takes about 660 mL of 12.5% liquid chlorine.
Chemical doses
Doses scale directly with volume: 1 ppm means one gram of a substance per cubic metre (1,000 litres) of water. Liquid chlorine at 12.5% delivers about 1 ppm of free chlorine per 8 mL per m³; cal-hypo at 65% about 1 ppm per 1.5 g per m³. Baking soda raises total alkalinity by 10 ppm at about 17.8 g per m³. Shocking usually means taking free chlorine to about 10 ppm. These are the rules of thumb in most pool-care guides; product labels are more specific and win when they differ.
Uses for the number
Filling: at a typical 9 gallons a minute from a hose, a 20,000-gallon pool takes about 37 hours, and the water utility will notice. Pump sizing: the pump should turn the full volume over once in 8–10 hours. Heaters are sized by volume and desired temperature rise, and the bag of salt for a chlorine generator is 3,200 ppm of the volume.
Frequently asked questions
How many gallons is my pool?
Length × width × average depth × 7.48 for a rectangle in feet. A 32 × 16 ft pool averaging 5.75 ft deep holds about 22,000 gallons. Enter your shape and dimensions above.
How do I find the average depth?
Add the shallow-end and deep-end depths and divide by two. For a flat-bottom pool, the depth is the average.
How long does it take to fill a pool?
Gallons ÷ hose flow rate. A garden hose delivers 6–12 gallons a minute, so a 20,000-gallon pool takes 28–55 hours. Two hoses halve it; a water delivery truck does it in an hour or two.
How much chlorine do I add?
To raise free chlorine by 1 ppm: about 8 mL of 12.5% liquid chlorine, or 1.5 g of 65% cal-hypo, per cubic metre of water. The chemical table above shows the amounts for your pool.
How much salt does a salt pool need?
Most chlorine generators want about 3,200 ppm: 3.2 kg per cubic metre, or roughly 27 lb per 1,000 gallons. For 22,000 gallons that is about 590 lb.
Sources
- CDC Model Aquatic Health Code: pool volume and water chemistry
- Trouble Free Pool: Pool math and dosing
By Calcelate Team. Formula from the sources above.
- 2026-09-14 · Formula and texts checked