How to use this calculator
Enter the flow rate and the fluid. For a pump moving liquid between two open tanks, give the elevation difference between the free surfaces and the head loss in the pipes; the pressure and velocity terms are then zero. If the pump head is already known, choose “Given directly”. Add the pump efficiency, and the motor efficiency if the electrical power is wanted.
Formulas
Worked example
0.05 m³/s of water lifted 30 m with 5 m of pipe losses, 75% pump (the default)
- hp = 30 + 0 + 0 + 5 = 35 m.
- Ph = 998 × 9.807 × 0.05 × 35 = 17.13 kW.
- Pshaft = 17.13 / 0.75 = 22.84 kW (30.6 hp).
Frequently asked questions
What is the difference between hydraulic and brake power?
Hydraulic (water) power is the energy actually given to the fluid. Brake or shaft power is what the motor must put into the pump shaft; it is larger because the pump loses some to friction and leakage.
Where do I get the head loss?
From the Darcy–Weisbach equation for each pipe plus the fittings; the pipe pressure drop calculator on this site gives it for a straight run.