Pump Specific Speed Calculator

Calculate pump specific speed from rotational speed, BEP flow rate and head.

Calculator

Specific speed (Ns) —

Formula

The metric pump specific speed is calculated using Q in m³/h:

Ns = N · √Q / H3/4

Where:

  • Ns = pump specific speed
  • N = rotational speed [rpm]
  • Q = BEP flow rate at maximum impeller diameter [m³/h]
  • H = head per stage at the same BEP [m]

Engineering note

For pump comparison, use the BEP flow rate and head at the maximum impeller diameter—not the rated duty point. For multistage pumps, use the head per stage. This calculator uses the metric convention with N in rpm, Q in m³/h and H in m. Always verify which convention is required by your project, company standard or customer specification.