What the result helps you understand
A pump can meet the required flow and head while still having an inadequate suction condition. NPSH margin is often driven by liquid level, suction losses, vapour pressure and the actual pump curve.
Pumps & Hydraulics
Pump Power & NPSH Calculator
Estimate hydraulic and shaft power, NPSH available and margin against the pump manufacturer's NPSH required value.
“The pump duty point looks achievable. Does the suction arrangement provide enough NPSH margin to avoid cavitation?”
Core formulae
Pump power and NPSH reference
Hydraulic power
P_h = ρ g Q HShaft power
P_shaft = P_h / η_pumpNPSH available
NPSH_a = (P_surface − P_vapour)/(ρg) + z_s − h_LNPSH margin
Margin = NPSH_a − NPSH_rNPSH required comes from the specific pump curve at the selected duty point. The acceptable additional margin is a project, owner or manufacturer decision.
Simple arrangement sketch
Open suction source to pump
1
Enter the pump duty point
Power is based on operating flow, total dynamic head, fluid density and pump efficiency.
2
Define the suction-side NPSH basis
Use absolute pressures. Positive static head means the liquid level is above the pump datum; negative means suction lift.
NPSH required is not calculated here
Enter NPSHr from the specific pump curve at the selected duty point. This tool only estimates what the suction arrangement can provide and compares the remaining margin.
Results
Power and suction margin
Required shaft power24.52 kW
Hydraulic power17.16 kW
Available pressure head above vapour pressure10.1 m
NPSH available11 m
NPSH margin above NPSHr8 m
Margin relative to entered requirement7 m
The calculated NPSH margin meets the entered project margin
Screening excess: 7 m. Confirm the pump curve, operating range, transient conditions and suction-system assumptions.
Method
Hydraulic power = ρgQH; shaft power divides by pump efficiency. NPSHa = pressure head above vapour pressure + static suction head − suction losses.
Job-file record
Save the calculation, not just the number.
Copy a permalink that reloads these inputs, or download a PDF record with inputs, visible results, assumptions, a sensitivity note, date and disclaimer.
Know where the quick calculation stops
NPSH required must come from the specific pump manufacturer curve at the duty point. The calculator does not model transients, two-phase flow, inlet recirculation or every manufacturer margin rule.
Important boundary
A calculator can show the arithmetic. It cannot establish every requirement that applies.
Confirm the actual equipment, loading, materials, condition, jurisdiction, contractual requirements, standard edition and current project documentation before using the result for design, repair, testing or lifting decisions.
Ask an engineer about this calculation →