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Pump Affinity Laws Calculator — RPM, Flow, Head & Power
Predict centrifugal-pump flow, head and power after a speed change using the affinity laws.
Last updated: September 17, 2026
Results
RPM must be positive and baseline values non-negative
Formula, example and assumptions
Q2=Q1r; H2=H1r²; P2=P1r³, r=N2/N1.
Reducing speed from 1500 to 1200 rpm gives r=0.8: flow 80%, head 64% and power 51.2% of baseline.
- Pump geometry is unchanged and efficiency is treated as approximately constant.
- Large speed changes should be checked against the actual pump and system curves.
Frequently asked questions
What does this Pump Affinity Laws Calculator solve?
Predict centrifugal-pump flow, head and power after a speed change using the affinity laws.
Which units should I use?
Use the SI units shown beside each input. The results also expose practical converted outputs where useful.
Can I use this for final equipment selection?
Use it for transparent engineering estimates and cross-checks. Confirm fluid properties, manufacturer curves and applicable design codes before final selection.