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Rectangular, Round and Oval: How Pool Shape Affects Volume
A rectangle uses length × width for its footprint. A circle uses π × radius². Oval mode assumes an ellipse, using π × half-length × half-width; it does not exactly model a kidney shape or straight-sided pool with rounded ends. For example, an 18-foot circular pool at a constant 4-foot water depth has about 1,017.876 cubic feet of water, or 7,614 US gallons.
Use equal depths for a flat bottom. Averaging the two ends fits a single linear slope, but a shallow shelf, separate deep well, steps or benches change the volume. Calculate suitable sections separately or use the builder's water-volume specification. The worked examples and reference tables explain how bottom geometry changes the result.
Use Volume Alongside Water Tests and Equipment Instructions
Volume is one input to maintenance planning. CDC's home-pool guidance emphasizes checking water chemistry and following manufacturer directions. Use the specific product's instructions and measured water conditions; products do not all use the same reference volume or dose. Enter actual water depth. Deliberately overstating volume is not a safety margin, and this calculator does not establish a chemical dose or swimming safety.
Volume divided by an assumed circulation time gives a theoretical flow rate: 20,000 gallons over a hypothetical 8 hours is about 41.7 gallons per minute. This is arithmetic, not a universal pump recommendation. Equipment selection also depends on plumbing resistance, manufacturer specifications and applicable requirements. Use model-specific instructions for filter media; the sand calculator estimates rectangular material volumes and does not model cylindrical filter tanks.
Frequently Asked Questions
How do I calculate pool volume in gallons?
For a rectangular pool, multiply length by width by average water depth, using feet, then multiply by 7.48052 for US gallons. For a circle, use π × (diameter ÷ 2)² × average depth. The oval mode uses an ellipse: π × (length ÷ 2) × (width ÷ 2) × average depth. Multiply either cubic-foot result by 7.48052.
Can I average the shallow and deep depths for every pool?
No. Equal depths describe a flat bottom; averaging the two ends fits a single linear slope. A pool with shallow shelves, steps or separate deep wells needs section-by-section volumes. Use actual water depth, not the pool-wall height.
Does oval mode fit every curved pool?
Oval mode assumes an elliptical footprint. A kidney-shaped pool or a pool with straight sides and rounded ends can have a different area. Use suitable separate sections or the builder's water-volume specification for a complex shape.
Does the volume result determine a chemical dose?
No. Volume is one input to maintenance planning. Use measured water conditions and the specific product's instructions; do not assume every product uses the same reference volume or dose. Deliberately overstating water depth is not a safety margin.
What conversion factors does this calculator use?
It multiplies cubic feet by 7.48052 for US liquid gallons, then gallons by 3.78541 for liters. The gallon factor is the rounded ratio 1,728 cubic inches per cubic foot divided by 231 cubic inches per US gallon. These are US gallons, not imperial gallons.
How can I estimate the time needed to fill a pool?
Divide the gallons needed by the measured fill rate in gallons per minute. For example, 20,000 gallons at a constant hypothetical 10 gallons per minute takes 2,000 minutes, or 33 hours 20 minutes. Actual flow can vary. Check your water supplier's filling restrictions and the pool manufacturer's instructions.
Sources for maintenance guidance