Suction Specific Speed Calculator

Calculate suction specific speed from rotational speed, BEP flow rate and NPSHr.

Calculator

API 610 basis: Use the BEP flow and the corresponding NPSHr at the maximum impeller diameter, not values at the rated duty point.

Suction specific speed (Nss) —

Formula

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

Nss = N · √Q / NPSHr3/4

Where:

  • Nss = suction specific speed
  • N = rotational speed [rpm]
  • Q = BEP flow rate at maximum impeller diameter [m³/h]
  • NPSHr = required NPSH at the same BEP [m]

Engineering note

For pump comparison, use the BEP flow rate at the maximum impeller diameter—not the rated duty point—and the corresponding NPSHr (commonly NPSH3). For a double-suction impeller, use one half of the total pump flow because Q is taken per impeller eye. This calculator uses the metric convention with N in rpm, Q in m³/h and NPSHr in m. Verify the required convention against the applicable standard or customer specification.