Pool Calculator
Volume, Chlorine, pH & Chemical Dosing
Calculate swimming pool water volume in gallons for any pool shape — rectangular, oval, round, kidney, and L-shaped. Uses volume to calculate correct chlorine, shock, alkalinity adjustment, stabilizer, and pH balancing chemical doses with turnover rate and pump run time.
Pool Volume Formula
Pool volume in gallons is calculated by multiplying surface area (in square feet) by average depth (in feet), then by 7.48 gallons per cubic foot. For pools with variable depth, use the average of shallow and deep end depths. Irregular shapes like kidney pools use a shape factor (approximately 0.82) to account for the curved areas.
Ideal Water Chemistry Targets
| Parameter | Ideal Range | Effect if Off |
|---|---|---|
| pH | 7.2–7.6 | Low: corrosive. High: chlorine ineffective. |
| Free Chlorine | 1–3 ppm | Low: algae/bacteria. High: skin irritation. |
| Total Alkalinity | 80–120 ppm | Stabilizes pH from swinging. |
| Calcium Hardness | 200–400 ppm | Low: etches plaster. High: cloudy water, scaling. |
| Cyanuric Acid (CYA) | 30–50 ppm | Protects chlorine from UV degradation. |
| Salt (saltwater only) | 2,700–3,500 ppm | Low: chlorinator underproduces. |
Saltwater vs Chlorine Pools
Saltwater pools still use chlorine — a salt chlorine generator (SWG) electrolyzes the salt water to produce chlorine automatically. Saltwater pools are gentler on skin and eyes, require fewer chemical purchases, and have lower long-term operating costs, but the SWG equipment costs $600–$2,000 upfront and may need replacement every 3–7 years.
What Is the Pool Calculator?
This pool volume calculator computes how many gallons or liters your swimming pool holds, the number every other pool task depends on: chemical dosing, pump and filter sizing, heater selection, and water bills. It handles rectangular, circular, oval, and variable-depth pools using average depth, and converts among gallons, liters, and cubic feet. One cubic foot holds 7.48 US gallons, and an average backyard in-ground pool holds 15,000–25,000 gallons.
Pool Calculator Example
A rectangular pool 32 ft long and 16 ft wide slopes from 3.5 ft to 8 ft deep.
Average depth = (3.5 + 8) ÷ 2 = 5.75 ft. Volume = 32 × 16 × 5.75 = 2,944 cubic feet × 7.48 = 22,021 gallons (about 83,400 liters).
That number drives everything: a pump should turn it over in about 8 hours (≈ 46 gallons per minute), raising free chlorine by 1 ppm takes about 29 oz of 12.5% liquid chlorine, and heating it 10°F requires roughly 1.8 million BTU.
Understanding Pool
Turnover, Filtration, and Water Clarity
Volume determines turnover time, how long the pump takes to move the entire pool through the filter. The 8-hour standard means all water is filtered roughly once per day (mixing means some water circulates repeatedly while some lags). Cloudy-water problems are most often turnover problems: an undersized pump, a clogged filter, or too few run hours for the actual volume.
Heating Costs Scale with Volume
Raising water temperature takes 8.34 BTU per gallon per °F. For a 20,000-gallon pool, a 10°F rise costs about 1.67 million BTU, several hours of a 400k BTU gas heater, before accounting for surface heat loss. A cover is the highest-ROI accessory a pool owner can buy: evaporation is the dominant heat-loss mechanism, and a cover cuts it dramatically while also halving chemical consumption.
Salt Systems and Volume Precision
Saltwater chlorination makes volume accuracy matter even more: target salinity is typically 3,200–3,400 ppm, and each 1,000 ppm adjustment on a 20,000-gallon pool takes about 167 lb of salt. Overshooting requires draining and refilling to correct. When in doubt between two volume estimates, dose for the smaller one and re-test, adding more is easy, removing is expensive.
Frequently Asked Questions
How do I calculate pool volume for a variable-depth pool?
Use average depth: (shallow end + deep end) ÷ 2, then multiply by surface area and 7.48 to get gallons. For pools with a long shallow shelf or diving well, split the pool into sections, compute each separately, and add them, the single-average shortcut misestimates strongly asymmetric pools.
How many gallons is a typical pool?
Common in-ground sizes: a 16×32 ft pool with 5 ft average depth holds about 19,200 gallons; 18×36 ft around 24,300; 20×40 ft around 30,000. Above-ground round pools: a 24 ft diameter at 4 ft deep holds about 13,500 gallons. Spas and hot tubs typically hold 300–500 gallons.
Why does pool volume matter for chemical dosing?
Every dosing chart is per 10,000 gallons. Raising free chlorine 1 ppm takes about 13 oz of 12.5% liquid chlorine per 10,000 gallons; raising alkalinity 10 ppm takes about 1.4 lb of baking soda per 10,000 gallons. An inaccurate volume estimate scales every dose wrong by the same percentage, chronically over- or under-treated water is usually a volume error, not a chemistry error.
What size pump do I need for my pool volume?
Standard practice is one full turnover in 8 hours: divide gallons by 480 to get the required gallons-per-minute. A 20,000-gallon pool needs about 42 GPM at your system's actual head pressure. Oversized pumps waste substantial electricity; a right-sized or variable-speed pump running longer at low speed filters better and cheaper.
How much water does a pool lose to evaporation?
Roughly 1/4 inch per day in warm dry weather, which on a 16×32 pool is about 80 gallons daily. Losing more than about 1/2 inch per day suggests a leak: try the bucket test, a bucket of water on a step should drop at the same rate as the pool; if the pool falls faster, call a leak service.
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