Enter your pool’s dimensions, total gallons, or a flow-and-head target to find the pump horsepower that will fully turn your water over in the time you set.
Related Calculators
Formula
The calculator uses three chained equations depending on which tab you select.
Required flow rate:
GPM = Volumegal ÷ (T × 60)
where T = turnover time in hours.
Brake horsepower:
BHP = (GPM × TDH) ÷ (3960 × η)
where TDH = total dynamic head in feet, η = pump efficiency (decimal).
Recommended pump size: the next standard HP rating (0.5, 0.75, 1.0, 1.5, 2.0, 2.5, 3.0) at or above the calculated BHP.
Interpretation
The result is the smallest off-the-shelf pump horsepower that can move your pool's volume through the filter within the turnover time you specified. Going bigger is not better — oversized pumps push water through the filter too fast to filter effectively and waste electricity.
- 0.5–1.0 HP: typical for small to mid-sized residential pools (under ~20,000 gal).
- 1.0–2.0 HP: typical for large residential pools or pools with spa jets and water features.
- 2.0–3.0 HP: very large residential or light commercial. Verify pipe sizing can handle the flow.
- Above 3.0 HP: commercial-grade sizing; consult a pool engineer.
A standard residential turnover is 8 hours. Health-code commercial pools often require 6 hours or less. If your calculated BHP is well below a standard size, a variable-speed pump run at reduced RPM is usually the most efficient pick.
Typical Pool Volumes and Pump Sizes
| Pool Size | Approx. Volume | Required GPM (8-hr turnover) | Typical Pump HP |
|---|---|---|---|
| 12 × 24 ft, 4.5 ft avg | ~9,700 gal | ~20 GPM | 0.5–0.75 HP |
| 16 × 32 ft, 5 ft avg | ~19,200 gal | ~40 GPM | 0.75–1.0 HP |
| 18 × 36 ft, 5.5 ft avg | ~26,700 gal | ~56 GPM | 1.0–1.5 HP |
| 20 × 40 ft, 6 ft avg | ~36,000 gal | ~75 GPM | 1.5–2.0 HP |
| 24 round, 4 ft | ~13,500 gal | ~28 GPM | 0.75 HP |
FAQ
What is total dynamic head (TDH) and what value should I use?
TDH is the total resistance your pump must push against — suction lift, vertical rise, pipe friction, filter losses, and heater or feature losses combined, measured in feet of water. Most residential in-ground pools fall between 40 and 60 ft TDH; 50 ft is a reasonable default if you don't have a measured value.
Why does the calculator recommend a higher HP than the brake HP number?
Pumps are sold in standard sizes (0.5, 0.75, 1.0, 1.5, 2.0 HP, etc.), so the result rounds up to the next available size. A calculated 1.2 BHP will be filled by a 1.5 HP pump.
Can a pool pump be oversized?
Yes. An oversized pump exceeds your filter's design flow rate, reducing filtration quality, straining plumbing, increasing noise, and raising electricity costs. Size to your turnover target, not to the biggest pump that fits.
What turnover time should I enter?
Use 8 hours for standard residential pools, 6 hours for heavily used pools or those with children and pets, and 4 hours to meet most commercial health codes. Shorter turnover times require more GPM and therefore more horsepower.