Pump Power Calculator
This pump power calculator finds the hydraulic power, shaft power, and horsepower a pump needs from the flow rate, head, fluid density, and efficiency. Enter them and the pump power calculator returns the power in watts, kilowatts, and HP. It applies the formula for pump power used for water and other liquids.
Results
The Pump Power Calculator is part of our Fluids collection. Browse more fluids to size, convert, and check your work alongside this tool.
What the pump power calculator shows
A pump adds energy to a fluid to lift it and push it through pipes, and the pump power calculator works out how much power that takes. It finds the hydraulic power from the flow and head, then divides by the efficiency to give the shaft power the motor must supply. As a centrifugal pump power calculator it reports watts, kilowatts, and horsepower.
The formula for pump power
The formula for pump power multiplies density, gravity, flow, and head for the hydraulic power, then divides by efficiency:
ρ is the density, g is 9.81, Q is the flow in cubic metres per second, and H is the head in metres. The flow in m³/h is divided by 3600 first. This power of pump equation gives the hydraulic power the fluid gains; the shaft power is higher because no pump is fully efficient.
Pump power calculator example
Water at 10 m³/h against a 20 m head with a 70 percent efficient pump. The pump power calculator gives:
So the pump needs about 0.78 kW at the shaft. Change the head and the pump power calculator updates the power at once.
How to use the pump power calculator
Enter the flow rate in cubic metres per hour, the head in metres, the fluid density, and the pump efficiency as a decimal, then the pump power calculator returns the hydraulic and shaft power. Use 1000 kg/m³ for water and an efficiency near 0.7 for a typical pump. The head is the total lift plus the friction losses the pump must overcome.
Reading the pump power calculator result
The hydraulic power is the energy the fluid gains; the shaft power is what the motor must deliver, always higher because of pump losses. Size the motor above the shaft power, since motors are rated in standard steps and need a margin for startup and wear. The horsepower figure suits pump catalogues, while kilowatts suit electrical sizing. A pump kw calculation like this is a starting point; add extra head for fittings and future fouling before you buy.
When to use the pump power calculator
- Sizing a motor with the pump power calculator
- Finding the shaft power from flow and head
- Rating a centrifugal pump power calculator result in HP
- Doing a pump kw calculation for an electrical supply
Common pump power calculator mistakes
- Using only the static lift. The head must include friction losses, not just the height.
- Ignoring efficiency. The shaft power is higher than the hydraulic power; size the motor on the shaft power.
- Wrong flow units. Enter m³/h; the formula converts it to m³/s.
Tips for pump sizing
- Add friction head to the static lift for the total head.
- Size the motor above the shaft power with a margin.
- Use the pump curve efficiency rather than a guess when you can.
The formula for power of pump and hydraulic power
The formula for power of pump rests on a simple idea: power is the rate of doing work, and a pump does work by lifting a mass of fluid each second against gravity. Multiply the density by the flow to get the mass per second, by gravity and the head to get the energy per second, and you have the hydraulic power. That is the hydraulic power formula for pump work, and it is why both a higher flow and a higher head raise the power in direct proportion. The power of a pump formula then divides by efficiency, because friction, leakage, and turbulence inside the pump mean the shaft must supply more than the fluid receives. Calculating hydraulic horsepower is the same figure in imperial units, water horsepower being the hydraulic power before losses.
Pump shaft power calculation and brake horsepower
Pump shaft power calculation and pump brake horsepower calculation describe the same number, the power at the pump shaft, in kilowatts or horsepower. It is always larger than the hydraulic power by the efficiency factor, so a pump at 70 percent needs its shaft to deliver about 1.4 times the fluid power. The motor is then sized above the shaft power, with a margin, and rated in standard frame sizes, which is where a pump kw calculation feeds into the motor choice. The head you use matters as much as the flow: it is the static lift plus the friction losses in the pipe, so pair this with the pressure loss calculator to build the total head before sizing the pump.
Pump power formula in kw reference
Shaft power for water at a 70 percent efficiency by flow and head, from the pump power formula in kw:
| Flow | Head | Hydraulic power | Shaft power |
|---|---|---|---|
| 5 m³/h | 20 m | 0.27 kW | 0.39 kW |
| 10 m³/h | 20 m | 0.55 kW | 0.78 kW |
| 10 m³/h | 40 m | 1.09 kW | 1.56 kW |
| 20 m³/h | 30 m | 1.64 kW | 2.34 kW |
Pump Power Calculator FAQ
What is the formula for pump power?
Hydraulic power = density times gravity times flow times head; shaft power = hydraulic power divided by efficiency. The pump power calculator applies both.
What is the difference between hydraulic and shaft power?
Hydraulic power is the energy the fluid gains. Shaft power is what the motor supplies, higher by the pump losses, so shaft power equals hydraulic power divided by efficiency.
How do I convert pump power to horsepower?
Divide the watts by 745.7. The calculator does this, so calculating hydraulic horsepower or shaft horsepower needs no extra step.
What efficiency should I use?
About 0.7 for a typical centrifugal pump, higher for a large well matched pump and lower for a small one. Read it from the pump curve when you can.