How the pool volume calculator works
Almost every pool job starts from the volume: dosing chemicals, sizing a pump and filter, choosing a heater or budgeting the water bill for a refill. The calculator takes the surface area of the water, multiplies it by the average depth, and converts the answer to litres or US gallons.
Volume = surface area × (shallow depth + deep depth) ÷ 2The surface area is length × width for a rectangle, π ÷ 4 × diameter² for a round pool and π ÷ 4 × length × width for an oval. Averaging the two ends is exact for a floor that slopes evenly and close enough for most hopper-bottom pools. One cubic metre holds 1,000 litres; one cubic foot holds 7.48 US gallons. For the chlorine dose, raising 1 m³ by 1 ppm takes 1 g of available chlorine, which is then divided by the strength of the product you use.
Worked example
An 8 × 4 m in-ground pool is 1.0 m deep at the steps and 2.0 m at the deep end, so its average depth is 1.5 m. The water surface is 32 m², giving 32 × 1.5 = 48 m³, or 48,000 litres (about 12,680 US gallons). To lift free chlorine by 2 ppm you need 48 × 2 = 96 g of available chlorine. Calcium hypochlorite at 65% supplies that in 96 ÷ 0.65 = 147.7 g of granules; liquid chlorine at 12.5% would take 768 mL.
Volumes of common pool sizes
| Pool | Water depth | US gallons | Litres |
|---|---|---|---|
| Round 12 ft (3.66 m) above-ground | 3 ft | 2,540 | 9,600 |
| Round 18 ft (5.5 m) above-ground | 4 ft | 7,610 | 28,800 |
| Round 24 ft (7.3 m) above-ground | 4 ft | 13,540 | 51,200 |
| Oval 15 × 30 ft | 4 ft | 10,580 | 40,000 |
| Rectangle 16 × 32 ft | 3.5–6 ft | 18,190 | 68,900 |
| Rectangle 20 × 40 ft | 3.5–8 ft | 34,410 | 130,300 |
Chlorine strength per 1 ppm
| Product | Per 10 m³ for +1 ppm | Per 10,000 US gal for +1 ppm |
|---|---|---|
| Calcium hypochlorite 65% | 15 g | 2.1 oz |
| Dichlor 56% | 18 g | 2.4 oz |
| Trichlor 90% | 11 g | 1.5 oz |
| Liquid chlorine 12.5% | 80 mL | 10.2 fl oz |
These are theoretical figures. Sunlight, swimmers and organic debris consume chlorine, so the real rise is often lower; retest after the pump has circulated the water for a few hours. Typical target ranges are 1–3 ppm free chlorine in a residential pool, but follow the label of your product and any local rules.
Practical tips
- Measure the water line, not the wall. An above-ground pool with 52 in walls usually holds about 46–48 in of water.
- Treat the result as an estimate. Steps, benches and rounded corners reduce the volume a few percent; a water meter reading during a refill is the only exact figure.
- Know what each product adds. Dichlor and trichlor raise stabiliser (cyanuric acid), calcium hypochlorite raises calcium hardness, and liquid chlorine raises pH slightly.
- Never mix chlorine products or add water to chemicals; pre-dissolve granules in a bucket of pool water only if the label says so, and store them dry and apart from acids.
A reproducible calculation with complete inputs
For a reproducible pool volume calculator example, use the metric input system and enter Pool shape: Rectangular; Length or diameter: 8 m; Width: 4 m; Water depth, shallow end: 1.0 m; Water depth, deep end: 2.0 m; Raise free chlorine by: 2 ppm; Chlorine product: Calcium hypochlorite 65% (granules). These settings describe one specific scenario, not a new default for every job. The result follows the method and allowances already explained above. Keep the entire set of values when comparing it with a hand calculation; omitting a selected material or an allowance can change the result even when the dimensions match. The following rows show the unrounded calculation values alongside the precision used by the interface.
| Result | Calculation value | Displayed value | Unit |
|---|---|---|---|
| Pool volume | 48000 | 48000 | L |
| Volume in cubic metres | 48 | 48.0 | m³ |
| Chlorine product for this dose | 147.692307692 | 148 | g |
| Water surface area | 32 | 32.0 | m² |
| Average depth | 1.5 | 1.50 | m |
Frequently asked questions
How many gallons are in a 16x32 pool?
A 16 × 32 ft pool running from 3.5 ft to 6 ft deep has an average depth of 4.75 ft, so it holds 512 × 4.75 × 7.48 ≈ 18,200 US gallons.
How many litres are in an 8 x 4 m pool?
With 1 m of water at one end and 2 m at the other, an 8 × 4 m pool holds 48 m³, which is 48,000 litres.
How do I calculate the volume of a round pool?
Multiply 0.785 × diameter × diameter × water depth. An 18 ft round pool with 4 ft of water holds 0.785 × 18 × 18 × 4 × 7.48 ≈ 7,610 gallons.
How much chlorine do I need for a 10,000 gallon pool?
To raise free chlorine by 1 ppm, use about 2 oz of 65% calcium hypochlorite or 10 fl oz of 12.5% liquid chlorine. A 3 ppm shock top-up needs three times that.
How long does it take to fill a pool?
Divide the volume by the flow of your hose: a garden hose delivers roughly 15–35 L (4–9 gal) per minute depending on pressure and diameter, so 48,000 litres takes about 23–53 hours.