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Pool Capacity
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⚠️ Disclaimer: This calculator estimates pool volume using average depth. Actual volume may vary by pool shape irregularities, step features, and benches. Always consult a pool professional for exact chemical dosing. Never add chemicals without testing water first.
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Sources & Methodology
Volume formulas and US gallon conversion verified against NIST unit standards. Pool volume methodology follows Pool & Hot Tub Alliance (PHTA) guidance for residential pool capacity calculations.
Pool & Hot Tub Alliance (PHTA) — Technical Resources
Industry standard for pool volume calculations, chemical dosing, and pump sizing used by pool professionals
NIST — Unit Conversions
1 US gallon = 231 cubic inches exactly. 1 cubic foot = 7.48052 US gallons.
Methodology: Rectangular: V = L × W × D (cu ft). Round: V = π × (d/2)² × D. Oval: V = π × (L/2) × (W/2) × D. Average depth = (shallow + deep)/2. US gal = cu ft × 7.48052. UK gal = cu ft × 6.22882. Litres = cu ft × 28.3168. Metric: multiply m³ by 264.172 for US gal. Turnover: pump GPM = volume / (target hours × 60).
⏱ Last reviewed: April 2026
How to Calculate Pool Volume in Gallons in 2026
Pool volume is essential for correct chemical dosing, pump sizing, and heating calculations. The formula depends on the pool shape. For rectangular pools, multiply length × width × average depth, then convert cubic feet to gallons. For round pools, use the circle area formula (πr²) multiplied by depth. Oval pools use the ellipse area formula.
Pool Volume Formulas
Rectangular: V(gal) = L × W × D × 7.481
Round: V = π × (d/2)² × D × 7.481 | Oval: V = π × (L/2) × (W/2) × D × 7.481
Average depth = (shallow end + deep end) / 2
Average depth = (shallow end + deep end) / 2
Common Pool Sizes and Volumes
| Pool Size | Avg Depth | US Gallons | Litres |
|---|---|---|---|
| 12 × 24 ft rect | 4.5 ft | 9,703 | 36,723 |
| 16 × 32 ft rect | 5 ft | 19,149 | 72,445 |
| 18 × 33 ft rect | 5 ft | 22,246 | 84,177 |
| 20 × 40 ft rect | 5.5 ft | 32,912 | 124,554 |
| 15 ft round | 48 in (4 ft) | 5,286 | 20,005 |
| 18 ft round | 52 in (4.33 ft) | 8,316 | 31,483 |
| 24 ft round | 52 in (4.33 ft) | 14,776 | 55,934 |
Pool Chemical Dosing Guide
Knowing your pool volume lets you calculate correct chemical doses. As a general guide for initial chlorination: add 1–3 lbs of granular trichlor per 10,000 gallons to reach 1–3 ppm free chlorine. For shocking: add 1 lb of calcium hypochlorite (65%) per 10,000 gallons to raise chlorine by approximately 7 ppm. Always test first and follow product label instructions — these are estimates only.
Pump Sizing and Turnover Rate
A residential pool should turn over its entire volume every 6–8 hours. Required pump flow in GPM = Pool volume (gal) ÷ (target turnover hours × 60). For a 20,000 gallon pool with 8-hour target: 20,000 ÷ 480 = 41.7 GPM minimum. Size your pump at 1.5× this rate to allow for filter resistance and pipe friction losses.
💡 Tip for variable-depth pools: Average depth = (shallow end + deep end) / 2 only works for pools with a uniform slope from one end to the other. For pools with a flat bottom and a single step down, calculate the shallow and deep sections separately and add the volumes.
Frequently Asked Questions
Rectangular: length x width x average depth x 7.481. Round: pi x (diameter/2) squared x depth x 7.481. Oval: pi x (length/2) x (width/2) x depth x 7.481. Average depth = (shallow + deep) / 2.
16 x 32 ft at 5 ft average depth: 16 x 32 x 5 x 7.481 = 19,149 US gallons (72,445 litres). At 4.5 ft: 17,234 gallons. At 6 ft: 22,979 gallons.
15 ft diameter (radius 7.5 ft) at 48 inches (4 ft): pi x 56.25 x 4 x 7.481 = 5,286 US gallons. At 52 inches (4.33 ft): 5,726 gallons.
24 ft diameter at 52 inches (4.33 ft): pi x 144 x 4.33 x 7.481 = 14,636 US gallons (55,395 litres).
Average depth = (shallow end depth + deep end depth) / 2. For 3 ft shallow and 8 ft deep: average = 5.5 ft. This formula assumes a uniform slope from one end to the other — use it for most standard residential pools.
12 x 24 ft at 5 ft average depth: 12 x 24 x 5 x 7.481 = 10,773 US gallons. At 4 ft: 8,618 gallons. At 4.5 ft: 9,696 gallons.
In metres: volume (m3) = length x width x depth. Litres = m3 x 1,000. For 10 m x 5 m x 1.5 m: 75 m3 = 75,000 litres. In feet: cubic feet x 28.3168 = litres.
At 9 gallons per minute (typical garden hose), a 20,000 gallon pool takes 20,000 / 9 = 37 hours. At 15 GPM (3/4 inch supply line at good pressure): about 22 hours. Check your hose flow rate by timing how long it takes to fill a known container.
For initial chlorination: 1 to 3 lbs of granular chlorine per 10,000 gallons to reach 1-3 ppm. For a 20,000 gallon pool: 2 to 6 lbs initially. Maintenance: 1 to 2 lbs per 10,000 gallons per week. Always test water before adding chemicals.
Turnover rate is how long the pump takes to circulate the entire pool volume once. Target is 6 to 8 hours for residential pools. Required GPM = pool volume / (hours x 60). For 20,000 gallons at 8 hours: minimum 41.7 GPM pump flow needed.
20 x 40 ft at 5 ft average depth: 20 x 40 x 5 x 7.481 = 29,924 US gallons. At 5.5 ft: 32,916 gallons. This is a large residential pool requiring 30 to 50 lbs of chemicals for initial treatment.
Oval volume = pi x (length/2) x (width/2) x depth x 7.481. For a 15 x 30 ft oval at 4 ft: pi x 7.5 x 15 x 4 x 7.481 = 10,572 US gallons.
Water weighs 8.34 lbs per US gallon. A 20,000 gallon pool contains 20,000 x 8.34 = 166,800 lbs of water (about 83.4 US tons or 75.7 metric tonnes). Pool structural integrity, decking, and foundation must all support this load.
Use a tape measure for length, width, and depth. Measure depth in the centre of the shallow and deep ends. For irregular shapes, break the pool into sections (rectangle + semicircle, etc.) and calculate each section separately, then sum the volumes.
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