AffinityQ · fluids

AffinityQ pump affinity flow

Predict GPM after a speed change before comparing pump or VFD options

TECHNICAL UTILITY · PUMP_AFFINITY_FLOW

Result

Enter values to begin.

Q2 = Q1 · (N2/N1) (affinity law for geometrically similar pump, speed change only)

How to use this estimate

Estimate new pump flow from affinity law when only shaft speed changes. How it works: Q2 = Q1 · (N2/N1) (affinity law for geometrically similar pump, speed change only). Out of scope: H2/H1=(N2/N1)²; P2/P1=(N2/N1)³; viscosity corrections; cavitation NPSH design. This is an approximate screening estimate, not a substitute for manufacturer charts or a full engineering design. Does not certify code compliance; confirm manufacturer data where it applies.

Sources, methodology, and assumptions

Methodology

Q2 = Q1 · (N2/N1) (affinity law for geometrically similar pump, speed change only)

Assumptions

Geometrically similar operation; Speed change only; Same fluid. This is an approximate screening estimate, not a substitute for manufacturer charts or a full engineering design.

Out of scope

H2/H1=(N2/N1)²; P2/P1=(N2/N1)³; viscosity corrections; cavitation NPSH design

Sources

NIST SP 811 — unit consistency context (not exact formula page) — NIST
NIST fluid / flow unit context — NIST

Last technically reviewed: 2026-09-11