Formula & worked example
Ns=N√Q/H^0.75 using rpm, US gpm and ft; nq uses m³/s and m.
A 1,750 rpm pump at 500 gpm and 100 ft head has US specific speed about 1,237, typical of radial-flow duty.
Plant engineering calculator · Updated Sep 17, 2026
Pump Specific Speed Calculator — US Ns, Metric nq & Impeller Class
Calculate centrifugal-pump specific speed from BEP speed, flow and head per stage. Returns US Ns, metric nq and a screening impeller-flow classification.
Inputs
Live result
US specific speed Ns 1,237.437
Metric specific speed nq 23.96033
Radial-flow screening range
Operating flow 100% of BEP
Flow deviation 0% from BEP
Inside common 70–120% BEP preferred operating screening range
Assumptions & limits
- Use flow and head at the best-efficiency point (BEP).
- For multistage pumps use head per stage; classification boundaries are approximate.
Frequently asked questions
What does this Pump Specific Speed Calculator calculate?
Calculate centrifugal-pump specific speed from BEP speed, flow and head per stage. Returns US Ns, metric nq and a screening impeller-flow classification.
Can I use the result for final equipment selection?
Use it for screening, benchmarking and option comparison. Final selection should use measured conditions, manufacturer performance data and applicable engineering standards.
Why are assumptions shown beside the calculation?
Plant calculations change materially with pressure basis, reference conditions, efficiencies and operating profile. Explicit assumptions make the result auditable instead of hiding those choices.