Pump Affinity Law Calculator
Select Input Mode (Speed or Diameter change). Enter baseline point. Calculates new Q₂, H₂, P₂. Export to Excel with live formulas.
Mode
Speed Change
Ratio used (r)
–
New Flow Q₂
– m³/h
New Head H₂
– m
New Power P₂
– kW
Formulas, units & assumptions
- Speed Change (D constant): Q₂ = Q₁·(n₂/n₁), H₂ = H₁·(n₂/n₁)², P₂ = P₁·(n₂/n₁)³
- Diameter Change (n constant): Q₂ = Q₁·(D₂/D₁), H₂ = H₁·(D₂/D₁)², P₂ = P₁·(D₂/D₁)³
- Results shown in the same units as inputs (Flow: m³/s, m³/h, L/s, gpm; Head: m, ft; Power: kW, HP; Diameter: mm, cm, m, inch).
- Assumes constant efficiency. For large changes, verify with pump curves.