Pump Horsepower Calculator
Flow and pressure in. The motor or engine your triplex pump needs, out.
Brake Horsepower Needed
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The Formulas
These are the pump-industry rules of thumb, the same ones Cat Pumps and Dultmeier publish.
Gas engine HP (standard) = GPM × psi ÷ 900
1460 is the pure hydraulic constant (1714) with 85% pump mechanical efficiency built in. A gas engine needs roughly twice the electric horsepower because gas engines are rated at peak, not continuous, output.
Motor Amps
Amps shown are full-load current for the next standard motor size up, from NEC Table 430.248 (single phase) and the NEC three-phase table (430.250). The circuit shown is the smallest standard breaker that covers 125% of that current. Use it to plan; your electrician sizes the actual circuit.
Reference Table
Electric horsepower, GPM × psi ÷ 1460. Works with JavaScript off.
| Flow | 650 psi | 800 psi | 1000 psi | 1200 psi | 1500 psi | 2000 psi |
|---|---|---|---|---|---|---|
| 1 GPM | 0.4 | 0.5 | 0.7 | 0.8 | 1.0 | 1.4 |
| 2 GPM | 0.9 | 1.1 | 1.4 | 1.6 | 2.1 | 2.7 |
| 3 GPM | 1.3 | 1.6 | 2.1 | 2.5 | 3.1 | 4.1 |
| 4 GPM | 1.8 | 2.2 | 2.7 | 3.3 | 4.1 | 5.5 |
| 5 GPM | 2.2 | 2.7 | 3.4 | 4.1 | 5.1 | 6.8 |
| 6 GPM | 2.7 | 3.3 | 4.1 | 4.9 | 6.2 | 8.2 |
| 7 GPM | 3.1 | 3.8 | 4.8 | 5.8 | 7.2 | 9.6 |
| 8 GPM | 3.6 | 4.4 | 5.5 | 6.6 | 8.2 | 11.0 |
| 10 GPM | 4.5 | 5.5 | 6.8 | 8.2 | 10.3 | 13.7 |
| 13 GPM | 5.8 | 7.1 | 8.9 | 10.7 | 13.4 | 17.8 |
Pressure is set by your nozzles, not the pump. A triplex pump moves a fixed GPM. The nozzles decide the psi. Size the nozzles on the nozzle number calculator, then come back here with that psi.
Sources: Cat Pumps handy formulas, Dultmeier horsepower requirements, NEC Tables 430.248 and 430.250.