Pump Specific Speed Calculator

Enter pump RPM, flow and head to find the specific speed.

How to use

  1. Enter your values in the fields above.
  2. Press Calculate to see your result instantly.
  3. Use the Share button to copy a link to your result.

About this calculator

Specific speed is a dimensionless-style index, N_s = N√Q ÷ H^0.75 in US units (N in rpm, Q in gpm, H in feet) or n_q in the equivalent metric form, that describes the shape of impeller a pump needs to deliver a given flow (Q) and head (H) at a given rotational speed (N) — independent of the pump's actual physical size.

Low specific speed values correspond to radial-flow impellers suited to high head and low flow, mid-range values to mixed-flow designs, and high values to axial-flow (propeller-type) impellers suited to high flow and low head. Mechanical and process engineers compute specific speed early in pump selection to identify the right impeller family for an application and to flag designs likely to suffer cavitation or efficiency problems before a pump is ever purchased.

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