Calculation reviewed: 4 October 2026 · Engineering Desk Tools
How to use the Pump hydraulic, shaft and motor power calculator
Estimate hydraulic power, pump shaft power and motor input power from flow, head, density and efficiencies. Start with measurements or documented values for the equipment and reporting period you actually want to assess. The calculator does not fill in a typical installation for you. Its blank fields help keep a demonstration value from being mistaken for your own operating data.
Choose the required options, enter the values in the labelled units and select Calculate. If a field is rejected, check its range and unit before changing it. The result is accompanied by the equation and assumptions so you can decide whether it answers your engineering question.
Inputs and measurement basis
- Flow rate (m³/h). Flow at the duty point, in m³/h.
- Total dynamic head (m). Total dynamic head: static lift plus pressure difference plus friction loss at this flow, in metres of liquid.
- Liquid density (kg/m³). About 998 kg/m³ for water at 20 °C. Use your liquid at its operating temperature. The value must be greater than zero.
- Pump efficiency at the duty point (%). Read from the pump curve at the duty point. Allowed range: 1 to 100.
- Motor efficiency at the duty point (%). From the motor data at the actual load; usually a little lower at partial load. Allowed range: 1 to 100.
Record the measurement source and operating condition. Retain unrounded values for verification.
Method and interpretation
Hydraulic power is the energy delivered to the liquid each second: density times gravity times volume flow times head. The pump shaft must supply more because the pump is not perfectly efficient, and the motor must draw more again because of its own losses. Pump efficiency should be taken from the pump curve at the real duty point.
Hydraulic power (kW) = ρ × g × Q × H / 1000, with Q in m³/s (m³/h ÷ 3600), g = 9.80665 m/s². Shaft power = hydraulic / pump efficiency. Motor input = shaft / motor efficiency.
Total dynamic head includes static lift, pressure difference and friction losses at the operating flow. Use the pump efficiency from the curve at the duty point, not the best-efficiency value, and the motor efficiency at the actual load. Drive and coupling losses are not included. Add margin for motor selection per the equipment standard and check NPSH separately.
Worked example
This example does not populate the form. Enter your own installation data.
Calculated result: 6.4729 kW motor input power. Estimate at the entered duty point. Select the motor from the pump curve at the maximum operating flow, with an appropriate margin.
Check the arithmetic independently using the displayed equation. Retain intermediate precision and compare the final value with your equipment documentation.
Quick-reference table
These illustrative rows retain the worked example assumptions except for the varied input. They are not certified ratings or manufacturer data. Use the form for intermediate values.
Common mistakes
Using pressure in bar as if it were head in metres; reading best-efficiency rather than duty-point efficiency; using water density for a heavier liquid; leaving out motor efficiency when estimating electrical demand; sizing the motor with no margin at the end of the curve. Before relying on the output, check the decimal format, unit scale and source of each value. Recheck unusual results against the formula.
Frequently asked questions
Are the example values used automatically?
No. Inputs remain blank when the tool opens or when you clear them. The worked example and table are reading material below the calculator. Enter the actual values you want to check each time, and label saved reports so their context is not lost.
What does the result mean?
The results trace power from the liquid back to the motor terminals. The motor input figure is the electrical demand at this duty point, which is useful for energy cost; select the motor with margin.
Can I use a zero or a negative value?
The allowed range follows the meaning of each input. A divisor needs a positive value; other fields may allow zero. Check the form labels and error message rather than forcing an invalid value. A rejected input must be corrected before a result can be shown.
Is this a final design or equipment approval?
No. Total dynamic head includes static lift, pressure difference and friction losses at the operating flow. Use the pump efficiency from the curve at the duty point, not the best-efficiency value, and the motor efficiency at the actual load. Drive and coupling losses are not included. Add margin for motor selection per the equipment standard and check NPSH separately. Use the calculation as support for a checked decision, and review equipment documentation and applicable requirements before changing an installation or operating setting.
How can I save or share a calculation?
Calculate first, then use Copy result or Print report. Some maintenance tools also provide a CSV summary. Reports contain your own entered data, so review them before sharing. You can share the public page URL without including plant records or confidential measurements.
How do I report an unexpected result?
Use the Contact page and include the tool URL, input values, units, expected output and the reference you used. Explain the measurement basis. Exclude confidential information.
Related tools and records
Use related calculations with consistent units, periods and equipment scope.
Embed this calculator
Copy this code into your website. The calculator stays free, with a visible attribution link. Visitors can use it without signing up.