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NPSHA Calculator

Net Positive Suction Head Available at the pump suction — the margin that protects a pump from cavitation.

Fluid · Pump Hydraulics
Version1.0.0MethodNPSHA
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Input Parameters

kg/m³
m
kPa(abs)
kPa(abs)
m
m
m

Estimate Vapor Pressure from Temperature

°C

Estimated P_v ≈ 2.330 kPa(abs)

2

Results

Ready to compute?

Enter your parameters and press Calculate NPSHA

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Reference Codes & Standards

  • ANSI/HI 9.6.1-2017

    Rotodynamic Pumps — Guideline for NPSH Margin

    Recommended NPSH margin ratios between NPSHA and NPSHR (NPSH3).

  • ANSI/HI 14.6-2016 / ISO 9906:2012

    Rotodynamic Pumps — Hydraulic Performance Acceptance Tests

    Defines NPSHR as the 3% head-drop point (NPSH3) used for the pump requirement.

  • API 610 12th Ed. / ISO 13709:2009

    Centrifugal Pumps for Petroleum, Petrochemical & Natural Gas

    Minimum NPSH margin requirements for process pump selection.

  • ANSI/HI 9.6.3-2017

    Rotodynamic Pumps — Guideline for Allowable Operating Region

    Suction conditions & operating-region limits affecting NPSH.

Further Reading

  • Karassik et al., Pump Handbook — NPSH fundamentals & suction design.
  • Cameron Hydraulic Data (Ingersoll-Rand) — vapor pressure & head loss data.
  • Perry's Chemical Engineers' Handbook — Antoine constants for vapor-pressure estimation.
  • NIST Chemistry WebBook — reference vapor-pressure data.
  • ANSI/HI standards — NPSH terminology and margin practice.

Engineering Tips

NPSHA is the absolute pressure head at the pump suction minus the liquid vapor pressure head.

  • Flooded suction: enter a positive value for zₛ.
  • Suction lift: enter a negative value for zₛ.
  • Absolute pressures: P_surf and P_v must be absolute, not gauge.

To avoid cavitation, keep NPSHA > NPSHR with a margin of 0.5–1.0 m (or per ANSI/HI 9.6.1).

Full formula with substituted values appears in the Calculation Breakdown.