Pump Power Calculator
Size a pump and estimate the electrical power it will draw at a given duty point.
In short
Size a pump and estimate the electrical power it will draw at a given duty point.
Formula: Ph = ρ × g × Q × H; Shaft power = Ph ÷ pump efficiency; Electrical input = Shaft power ÷ motor efficiency
Electrical input power
11.57 kW
- Hydraulic power
- 8.16 kW
- Shaft power
- 10.87 kW
- Flow in SI units
- 0.027778 m³/s
- Standard gravity used
- 9.80665 m/s²
Calculated from the values you entered. Formula version 1; last reviewed 2026-09-15.
What this calculator does
Hydraulic power from density, gravity, flow and head, divided by the efficiencies the engineer supplies. Standard gravity is the only constant used. Density and both efficiencies are entered by the engineer; no typical pump or motor efficiency is assumed.
Use it to turn Flow rate, Flow unit, Total head, Fluid density, and the other shown inputs into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this professional & industry calculation.
Inputs and what they mean
- Flow rate
- — number value.
- Flow unit
- — choice value.
- Total head
- — number value.
- Fluid density
- — number value.
- Pump efficiency
- — From the pump curve at this duty point..
- Motor efficiency
- — From the motor data sheet..
How to use it
- Enter your own figures — the calculator never fills in a rate, price or benchmark for you.
- Press Calculate to see the result.
- Read the formula, variables, assumptions and source below the result before you rely on it.
Formula
Ph = ρ × g × Q × H; Shaft power = Ph ÷ pump efficiency; Electrical input = Shaft power ÷ motor efficiency.
Inputs used: Flow rate, Flow unit, Total head, Fluid density, Pump efficiency, Motor efficiency.
Edge handling: Flow rate is required.; Flow rate must be greater than zero.; Flow rate must be no more than 1000000000.; Total head is required.; Total head cannot be negative..
Worked example
100 m³/h of water against 30 m of head
- Start with Flow rate: 100, Flow unit: m3_h, Total head: 30, Fluid density: 998, Pump efficiency: 75, Motor efficiency: 94.
- Apply the method: Ph = ρ × g × Q × H; Shaft power = Ph ÷ pump efficiency; Electrical input = Shaft power ÷ motor efficiency.
- Pump at 75% efficiency driven by a 94% efficient motor.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- Inputs outside the supported range are rejected rather than forced into a result.
- The result depends on the values you enter for this pump power calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Reference: U.S. Department of Energy — Improving pumping system performance: a sourcebook for industry
Last reviewed:
Common questions
Where does this formula come from?
Improving Pumping System Performance: A Sourcebook for Industry, U.S. Department of Energy. See the source link on this page.
What kind of calculation is this?
Hydraulic power from density, gravity, flow and head, divided by the efficiencies the engineer supplies. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.
What are its limits?
Power at one duty point only. It does not model system curves, NPSH or transient behaviour.
How do I use the Pump Power Calculator?
Enter the required values for Flow rate, Flow unit, Total head, Fluid density, Pump efficiency, and the other fields shown. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the Pump Power Calculator use?
Ph = ρ × g × Q × H; Shaft power = Ph ÷ pump efficiency; Electrical input = Shaft power ÷ motor efficiency The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone. Check the formula, example, and limitations on this page before using the result for a real professional & industry decision.
Can the Pump Power Calculator be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
Formula, source and verification
Hydraulic power from density, gravity, flow and head, divided by the efficiencies the engineer supplies.
The question it answers: How much power will this pump draw at the flow and head we need?
The formula
Ph = ρ × g × Q × H; Shaft power = Ph ÷ pump efficiency; Electrical input = Shaft power ÷ motor efficiency
- Q — Flow rate
- (m3_s). Volumetric flow at the duty point.
- H — Total head
- (m). Total dynamic head.
- ρ — Fluid density
- (kg/m³). Density of the pumped fluid, entered by the engineer.
- g — Gravitational acceleration
- (m/s²). 9.80665 m/s², the standard value.
- ηp — Pump efficiency
- (%). From the pump curve at the duty point.
- ηm — Motor efficiency
- (%). From the motor data sheet.
Units: m³/h or L/s in, metres of head, watts and kilowatts out.
What kind of calculation this is
Deterministic formula. The same inputs always give the same answer. The maths is fixed and does not depend on judgement.
Method
Standard gravity is the only constant used. Density and both efficiencies are entered by the engineer; no typical pump or motor efficiency is assumed.
Assumptions built into the result
- Operational: Incompressible fluid at the stated density.
- Industry: Standard gravity of 9.80665 m/s².
Figures this calculator will never guess for you
- No default pump efficiency, motor efficiency, safety factor or energy price is applied.
Limitations
- Power at one duty point only. It does not model system curves, NPSH or transient behaviour.
Source and version
- Standard or reference
- Pumping system power relationships — U.S. Department of Energy (Improving Pumping System Performance: A Sourcebook for Industry, U.S. Department of Energy.)
- Published source
- U.S. Department of Energy — Second edition
- Formula version
- Version 1
- Verification
- Reviewed against the cited source on
- How much weight the source carries
- Standards or government
- Applies to
- Currency
- The result is a ratio or index, so it does not depend on currency.
Cite this page
Free Calculator. (2026, September 15). Pump Power Calculator. https://freecalculator.tech/tools/pump-power-calculator
"Pump Power Calculator." Free Calculator, 15 Sept. 2026, https://freecalculator.tech/tools/pump-power-calculator.
Pump Power Calculator — Free Calculator, https://freecalculator.tech/tools/pump-power-calculator
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