Pump Power Calculator
Work out how much power a pump needs from its flow rate and head. Enter flow in cubic metres per second, head in metres, the fluid density and the pump efficiency, and the tool returns the hydraulic power delivered to the fluid and the shaft power the motor must supply. Results appear in both watts and kilowatts.
How to calculate pump power
- Enter the volumetric flow rate in cubic metres per second.
- Enter the total pump head in metres.
- Set the fluid density, leaving 1000 for water or changing it for another liquid.
- Set the pump efficiency as a fraction between 0 and 1.
- Read the hydraulic power and shaft power, each shown in kilowatts and watts.
Examples
Water pump, ideal efficiency
Q = 0.05 m3/s, head = 20 m, density = 1000, efficiency = 1
hydraulic power = 9806.65 W (9.80665 kW), shaft power = 9806.65 W
Same duty at 70 percent efficiency
Q = 0.05 m3/s, head = 20 m, density = 1000, efficiency = 0.7
shaft power = 14009.5 W (about 14.0095 kW)
Higher head at 80 percent efficiency
Q = 0.04 m3/s, head = 32 m, density = 1000, efficiency = 0.8
hydraulic 12552.512 W (12.552512 kW), shaft 15690.64 W (15.69064 kW)
Frequently asked questions
What is the pump power formula?
Hydraulic power equals density times g times flow rate times head, using g of 9.80665 m/s^2. Shaft power is that hydraulic power divided by the pump efficiency.
What is the difference between hydraulic and shaft power?
Hydraulic power is the useful power added to the fluid. Shaft power is the larger input power the motor must supply, because friction and leakage inside the pump waste some of it.
What efficiency should I use?
Use the manufacturer's value where possible. Many centrifugal pumps fall between 0.6 and 0.85. The default of 1 gives the ideal hydraulic power with no losses.
What units does the calculator use?
Inputs are SI: cubic metres per second for flow, metres for head and kg/m3 for density. Power is reported in both watts and kilowatts.
How do I get flow rate from litres per minute?
Divide litres per minute by 60000 to get cubic metres per second. For example, 3000 L/min is 0.05 m3/s.
Does the head include friction losses?
It should. Enter the total dynamic head, which sums the static lift, the friction losses in pipes and fittings, and any velocity head at the outlet. The tool uses whatever head you provide.
How do I convert the result to horsepower?
One mechanical horsepower is 745.7 watts, so divide the power in watts by 745.7. For instance, 9806.65 W is about 13.15 hp.
Can I use it for fluids other than water?
Yes. Change the density field to match the fluid, such as about 850 to 900 for many oils or 1025 for seawater. The rest of the formula stays the same.
Are my inputs sent to a server?
No. The maths runs in your browser, so the flow, head, density and efficiency you type never leave your device.
Learn more
- Hydraulic power vs shaft pump power
How rho g Q H gives hydraulic power, why efficiency raises it to shaft power, and how total dynamic head and kW to hp fit in.
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