Pool volume calculator
Same as shallow for a flat-bottom pool or spa.
Quick answer
Pool volume in gallons equals surface area in square feet × average depth in feet × 7.48. For a rectangle, surface area is length × width; for a circle, 0.785 × diameter²; for an oval, 0.785 × length × width. A 75 × 42 ft pool, 3.5 to 5 ft deep, holds about 100,000 gallons.
- 1 cubic foot of water = 7.48 US gallons; 1 gallon = 3.785 liters.
- Average depth = (shallow + deep) ÷ 2 for a uniform slope.
- Kidney pools: area ≈ 0.45 × (width A + width B) × length.
- Use the design volume on your permit when you have it.
Pool volume formulas by shape
| Shape | Gallons formula | Example | Volume |
|---|---|---|---|
| Rectangle | L × W × avg depth × 7.48 | 60 × 30 ft, 4 ft flat | 53,860 gal |
| Rectangle (sloped) | L × W × (shallow + deep) ÷ 2 × 7.48 | 75 × 42 ft, 3.5–5 ft | 100,145 gal |
| Round / spa | 0.785 × D² × depth × 7.48 | 8 ft spa, 3.5 ft deep | 1,316 gal |
| Oval | 0.785 × L × W × avg depth × 7.48 | 30 × 15 ft, 4.5 ft | 11,897 gal |
| Kidney | 0.45 × (A + B) × L × avg depth × 7.48 | 32 ft, A 16, B 10, 3.5–6 ft | 13,303 gal |
Why the volume matters for compliance
- Every chemical dose is calculated from volume — an error of 20% in volume is a 20% error in every dose. Plug your volume into the pool chemical calculator.
- Turnover rate is volume ÷ flow. Inspectors compare your flow meter reading to the turnover your code requires — see the turnover calculator.
- Fecal-incident hyperchlorination to 20 ppm needs a lot of chlorine in a large pool. Knowing the volume tells you whether you have enough product on hand.
- Your log header should show each pool’s volume so anyone on staff can calculate a dose.
Tips for irregular commercial pools
Split an L-shaped or freeform pool into rectangles and circles, calculate each part, and add them. Diving wells and hoppers hold more than a straight slope suggests, so calculate a deep section separately. The most reliable number is the design volume on the plans approved by your health department — use the calculator to sanity-check it.
How to calculate pool volume in gallons
- Measure the surface. Measure length and width (or diameter) in feet at the water line.
- Find the average depth. Add the shallow and deep depths and divide by 2.
- Calculate surface area. Rectangle: L × W. Circle: 0.785 × D². Oval: 0.785 × L × W. Kidney: 0.45 × (A + B) × L.
- Convert to gallons. Multiply surface area × average depth × 7.48 to get US gallons.
Frequently asked questions
How do I calculate how many gallons my pool holds?
Multiply surface area (square feet) by average depth (feet) by 7.48. For a 50 × 25 ft pool averaging 4.5 ft deep: 50 × 25 × 4.5 × 7.48 ≈ 42,075 gallons.
How many gallons is a 25-yard pool?
A 25-yard by 45-foot pool (75 × 45 ft) averaging 4.5 ft deep holds about 113,600 gallons. Six-lane 25-yard pools are commonly 75 × 42 ft and hold roughly 90,000–120,000 gallons depending on depth.
How many gallons is a commercial hot tub?
Most commercial spas hold 500–1,500 gallons. An 8 ft round spa 3.5 ft deep holds about 1,316 gallons. Subtract a little for seats and benches.
How do I convert pool gallons to liters?
Multiply gallons by 3.785. A 50,000-gallon pool is about 189,000 liters, or 189 cubic meters.
This page is an educational summary, not legal advice. Pool and spa codes differ by state and county and change over time — always confirm requirements with the health department that inspects your facility.