Plumbing & Fluid

Pump Power Calculator

Solve pump hydraulic, shaft and electrical power from a known duty point. Compare SI/US results and review the method, assumptions and related references below.

Change any input to update the calculation. Unit changes preserve the physical quantity.

CALCULATION SETUP

Inputs

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Results

Hydraulic output

0.3915 kW0.525 hp

Required pump shaft input

0.5593 kW0.75 hp

Electrical input

0.6214 kW0.8333 hp

Pump losses

0.1678 kW0.225 hp

Motor losses

0.0621 kW0.0833 hp

Volume flow

2 L/s120 L/min7.2 m³/h31.7006 GPM (US)4.2378 CFM

Head

20 m65.6168 ft

Overall efficiency

63 %

Calculation breakdown

Result interpretation
Solve pump hydraulic, shaft and electrical power from a known duty point

Assumptions & checks

A known-duty power balance, distinct from Pump TDH which determines system head. Efficiency is entered, not predicted from a pump curve; no NPSH or motor sizing approval.

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Where does this result go next?

Previous stepPump TDH Calculator

Calculate total dynamic head

Follow the full workflow: Pump system head and power check →

Formula

Solve pump hydraulic, shaft and electrical power from a known duty point

Phyd=ρgQH; Pshaft=Phyd/ηpump; Pelectric=Pshaft/ηmotor. Reverse flow or head uses the same entered efficiencies. Worked example: 998 kg/m³, 2 L/s and 20 m head: hydraulic power 391.481 W; at 70% pump and 90% motor efficiency electrical input is 621.399 W.

Worked example

Using the default values shown in the calculator, the same formula gives the following result. This is a quick sanity check for the calculation, not a design recommendation.

Inputs

Volume flow
2 L/s
Known total dynamic head
20 m
Fluid density
998 kg/m³
Pump efficiency
70 %
Motor efficiency
90 %

Result

Hydraulic output
0.3915 kW
Required pump shaft input
0.5593 kW
Electrical input
0.6214 kW
Pump losses
0.1678 kW
Motor losses
0.0621 kW
Volume flow
2 L/s
Head
20 m
Overall efficiency
63 %

REAL INPUTS · CLEAR METHOD

Practical worked examples

Illustrative scenarios using this page’s calculation or verified reference model. Change the assumptions for your own job.

2 L/s water pump at 20 m TDH

Given

Volume flow
2 L/s
Known total dynamic head
20 m
Fluid density
998 kg/m³
Pump efficiency
70 %
Motor efficiency
90 %
Calculation / lookup method

Phyd=ρgQH; Pshaft=Phyd/ηpump; Pelectric=Pshaft/ηmotor. Reverse flow or head uses the same entered efficiencies. Worked example: 998 kg/m³, 2 L/s and 20 m head: hydraulic power 391.481 W; at 70% pump and 90% motor efficiency electrical input is 621.399 W.

Result

Hydraulic output
0.3915 kW
Required pump shaft input
0.5593 kW
Electrical input
0.6214 kW
Pump losses
0.1678 kW
Motor losses
0.0621 kW
Volume flow
2 L/s

Hydraulic power uses ρgQH. Electrical power also includes the separate pump and motor efficiency assumptions.

5 L/s at 30 m TDH with 75% pump efficiency

Given

Volume flow
5 L/s
Known total dynamic head
30 m
Fluid density
998 kg/m³
Pump efficiency
75 %
Motor efficiency
92 %
Calculation / lookup method

Phyd=ρgQH; Pshaft=Phyd/ηpump; Pelectric=Pshaft/ηmotor. Reverse flow or head uses the same entered efficiencies. Worked example: 998 kg/m³, 2 L/s and 20 m head: hydraulic power 391.481 W; at 70% pump and 90% motor efficiency electrical input is 621.399 W.

Result

Hydraulic output
1.4681 kW
Required pump shaft input
1.9574 kW
Electrical input
2.1276 kW
Pump losses
0.4894 kW
Motor losses
0.1702 kW
Volume flow
5 L/s

TDH must already include static and system loss terms. Do not add the same friction loss again in this power-only tool.

50 US GPM at 60 ft head

Given

Volume flow
50 GPM (US)
Known total dynamic head
60 ft
Fluid density
998 kg/m³
Pump efficiency
70 %
Motor efficiency
90 %
Calculation / lookup method

Phyd=ρgQH; Pshaft=Phyd/ηpump; Pelectric=Pshaft/ηmotor. Reverse flow or head uses the same entered efficiencies. Worked example: 998 kg/m³, 2 L/s and 20 m head: hydraulic power 391.481 W; at 70% pump and 90% motor efficiency electrical input is 621.399 W.

Result

Hydraulic output
0.5646 kW
Required pump shaft input
0.8066 kW
Electrical input
0.8962 kW
Pump losses
0.242 kW
Motor losses
0.0896 kW
Volume flow
3.1545 L/s

The US units convert before the shared power calculation. Pump curve, NPSH and motor selection require their own review.

Technical references for this calculation

Reference lookupMotor kW & HP Conversion ChartReference lookupWater Pressure & Head ReferenceReference lookupWater Properties Table

Frequently asked questions

What does this result tell me?

A known-duty power balance, distinct from Pump TDH which determines system head. Efficiency is entered, not predicted from a pump curve; no NPSH or motor sizing approval.

How can I check the calculation?

Worked example: 998 kg/m³, 2 L/s and 20 m head: hydraulic power 391.481 W; at 70% pump and 90% motor efficiency electrical input is 621.399 W. Review each stated input and unit; use project-specific values rather than treating the editable example as a requirement.

Reference data & method sources

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