Pool Calculator uses Volume = length × width × average depth, or π × radius² × depth, to estimate pool gallons or liters, fill time, salt, chlorine dose, and heating energy from your pool size inputs.
This pool calculator estimates the water volume of a rectangular, square, circular, or round pool from its physical dimensions, then uses that volume to estimate fill time, initial salt requirement, liquid chlorine dose, and heating energy. Enter your measurement system, pool shape, and dimensions above to generate all five outputs at once.
The tool supports both US Customary (feet, gallons, BTU) and Metric (meters, liters, kWh) inputs, so you can work with whatever unit system matches your equipment and supplier.
How pool volume is calculated from dimensions
Rectangular & square pools
Volume is length × width × average depth. The result in cubic feet is then converted to US gallons by multiplying by 7.480519. For metric inputs the result is in cubic meters, then multiplied by 1,000 to get liters.
Circular & round pools
Volume uses the circle area formula — π × (diameter ÷ 2)² × average depth. Enter the full diameter, not the radius. The width field is hidden for circular pools because only one horizontal dimension is needed.
Average depth
If your pool has a shallow end and a deep end, measure both and average them: (shallow depth + deep depth) ÷ 2. Using a single point depth will over- or understate volume. Typical residential pools run 3–4 ft shallow, 5–6 ft deep — an average of about 4.5 ft.
Unit conversions used
1 cubic foot = 7.480519 US gallons (NIST). 1 cubic meter = 1,000 liters (exact SI definition). These multipliers are applied internally after the geometric volume is computed.
Formulas used by this calculator
Volume = Length × Width × Average Depth
Volume = π × (Diameter ÷ 2)² × Average Depth
US Gallons = Cubic Feet × 7.480519
Liters = Cubic Meters × 1,000
Fill Time (min) = Pool Volume ÷ Hose Flow Rate
Salt Required = Pool Volume × Salt Factor (ppm target)
Chlorine Volume = Pool Volume × Dose Factor (+10 ppm FC)
BTU for +1°F = US Gallons × 8.34
Worked example — 30 × 15 × 5 ft rectangular pool
Understanding each result
The primary output — pool water volume in US gallons or liters, plus cubic feet or cubic meters. All four secondary results depend on this number. The volume is calculated from geometry alone; it does not account for pump housings, steps, or other objects displacing water inside the pool.
Time to fill from empty at a fixed hose flow rate — 9 GPM (US) or 34 LPM (Metric), which approximates a standard garden hose at typical residential water pressure. Actual fill time varies with pipe diameter, supply pressure, and hose length. The output shows both total minutes and total hours for convenience.
Fill Time = Volume ÷ Flow RateThe estimated amount of pool-grade salt (NaCl) needed to bring fresh water to 3,200 ppm — the typical target for saltwater chlorine generators. The bag count assumes standard 40 lb bags (US) or 25 kg bags (Metric). This is a starting estimate for fresh water only. Test actual salinity before adding salt and adjust accordingly — existing tap water may already contain minerals that affect the true requirement.
Target: 3,200 ppmThe volume of 12.5% sodium hypochlorite solution needed to raise free chlorine by 10 ppm. This is a chemical shock estimate, not a maintenance dose. The dose factor is derived from the available chlorine content of 12.5% liquid chlorine products. Because chlorine demand varies with cyanuric acid level, temperature, and organic load, always test free chlorine before dosing and add chemicals in stages.
Boost target: +10 ppm FCThe theoretical thermal energy needed to raise the entire water volume by 1°F (US) or 1°C (Metric). For US units, the formula is US gallons × 8.34 BTU/°F, which reflects the specific heat capacity of water (1 BTU raises 1 lb of water 1°F, and water weighs 8.34 lb/gal). The heater time estimate uses a 100,000 BTU/h gas heater (US) or 30 kW electric heater (Metric) as a reference. Real heat-up time is longer due to heat loss to the environment, heater efficiency, and ambient temperature. Multiply the single-degree BTU output by the number of degrees you need to raise the water for a full heat-up estimate.
US: gallons × 8.34 BTU/°F · Metric: liters × 0.00116 kWh/°CAssumptions and limitations
1 Pool geometry
- The calculator models only two geometric shapes: rectangular and circular.
- L-shaped, kidney-shaped, freeform, or irregularly shaped pools cannot be accurately represented. For those, break the pool into simpler sections and add the volumes.
- Sloped walls (typical of vinyl liner pools), curved walls (fiberglass shells), and beach entries will produce a volume lower than the geometric estimate. Treat the output as a starting upper bound.
2 Average depth
- The depth field expects the average water depth across the entire pool, not the deepest point.
- For a pool with a uniform slope from 3 ft to 6 ft, enter 4.5 ft as the average depth.
- For a pool with distinct shallow and deep sections joined by a slope, a more precise average is: ((shallow length × shallow depth) + (deep length × deep depth) + slope section estimate) ÷ total length.
3 Chemical estimates
- Salt and chlorine outputs are volume-based estimates only. They assume fresh water at the standard baseline with no existing mineral or chemical content.
- Actual dosing requirements vary with source water chemistry, stabilizer (CYA) level, pH, total alkalinity, calcium hardness, and organic load.
- Always test pool water with a reliable test kit or strip before adding any chemical, and add chemicals in increments rather than all at once.
4 Fill time and heating
- Fill time assumes a constant 9 GPM (US) or 34 LPM (Metric) throughout the fill. Actual hose output varies with supply pressure and hose condition.
- Heating energy is a theoretical minimum. Real-world heat-up is slower due to evaporative loss, ambient air temperature, wind, and heater efficiency ratings typically in the 80–95% range for gas heaters.
- The heater time estimate uses an ideal (100% efficient) reference heater. Use it for comparison only, not scheduling.
Chemical safety: Pool salt and liquid chlorine outputs are planning estimates. Test your water before adding any chemical. Never add multiple chemicals simultaneously. Follow all label directions and local regulations for chemical storage, handling, and disposal.
References
- Unit Conversion · NIST NIST — SI Units: Volume Official source for cubic foot to gallon and cubic meter to liter conversions used in this tool.
- Energy · U.S. EIA U.S. EIA — British Thermal Units (BTU) Definition of BTU and its use in energy calculations for heating applications.
- Pool Chemistry · CDC CDC — Healthy Swimming: Pool Water Quality Public health guidance for safe pool water chemistry and disinfection principles.
- Salt Pools · APSP / Pool Industry Pool & Hot Tub Alliance (PHTA) Industry body providing guidance on saltwater pool salinity levels, chlorine generator operation, and water balance standards.
- Volume Estimation · NSF NSF — How to Calculate Pool Volume Methodology for estimating pool water volume from geometric shapes used as reference for the formulas in this tool.
- Chlorine Dosing CDC — Pool Chemical Safety Fact Sheet Guidance on safe handling and use of pool disinfection chemicals including liquid chlorine products.