How to use the Pump Power Calculator
- 1. Enter flowIn m³/h, L/s, L/min or m³/s.
- 2. Enter headTotal head in metres: static lift plus friction and fitting losses.
- 3. Add efficienciesGet hydraulic power, shaft power and motor input power.
Pump power formula
Hydraulic power Ph = ρgQH watts, with ρ in kg/m³, g = 9.81 m/s², Q in m³/s and H in m. The pump shaft (brake) power is Ph / ηpump, and the electrical input is shaft power / ηmotor. 1 HP = 0.7457 kW.
Total head = static suction lift + static delivery head + friction losses in pipes and fittings + any pressure head at the outlet.
Worked example and exam tips
A pump lifts 36 m³/h of water through 25 m. Q = 0.01 m³/s. Ph = 1000 × 9.81 × 0.01 × 25 = 2.45 kW. With 70% pump efficiency, shaft power = 3.50 kW. With a 90% motor, input = 3.89 kW.
- Convert flow to m³/s first; most mistakes come from m³/h.
- Choose the next larger standard motor size.
- For oils and other liquids, change the density.
- Pumps are often oversized; running far from the best efficiency point wastes energy, so size the head honestly instead of adding large margins.
Frequently asked questions
What is the difference between hydraulic and shaft power?
Hydraulic power is the energy given to the liquid. Shaft power is what the pump needs, which is more because of pump losses.
How do I find total head?
Add the vertical lift and the friction loss in the pipe (from the Darcy equation or a pipe chart) and fittings.
Which efficiency should I use?
Use the pump's efficiency at the duty point from its curve. The defaults are only starting values.
Is this calculator free?
Yes. You enter your name and WhatsApp number once to see your result, and all other Uncodemy tools then open without the form. Everything is calculated in your browser.