Pump Horsepower for Flow
HP = (GPM × ft head) / (3960 × pump efficiency).
Result
Required HP
0.583 HP
0.43 kW.
- Flow30 GPM
- Head50 ft
- Efficiency65.0%
- HP0.5828
- kW0.4346
- Annual energy (24/7)3,807 kWh/yr
Step-by-step
- HP = (GPM × head) / (3960 × η) = (30 × 50) / (3960 × 0.65) = 0.583.
- kW = HP × 0.7457 = 0.435.
How to use this calculator
- Enter required GPM and head.
- Pump efficiency from spec or 65% default.
About this calculator
Pump sizing: HP = (GPM × ft head) / (3960 × η). 3960 is unit conversion constant (water specific gravity built in). 30 GPM at 50 ft head with 65% efficient pump: ~0.58 HP. Add safety factor (10-25%) and round up to next standard size (1/2, 3/4, 1, 1.5, 2 HP). Centrifugal pumps run 60-75% efficient at design point; positive displacement 80-90%. Oversize hurts efficiency; undersize fails to meet demand.
Frequently asked
33,000 ft·lb/min/HP / 8.33 lb/gal = 3960 ft·gal/min/HP.
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