💧 Pump Affinity Laws Calculator
Flow, head, and power at changed speed or impeller diameter
Results at New Speed
Speed Ratio
—
N₂/N₁
New Flow Q₂
—
GPM / m³/h
New Head H₂
—
ft / m
New Power P₂
—
HP / kW
Affinity Laws
Q₂/Q₁ = N₂/N₁ (flow proportional to speed)
H₂/H₁ = (N₂/N₁)² (head proportional to speed squared)
P₂/P₁ = (N₂/N₁)³ (power proportional to speed cubed)
Replace N with D (diameter) for impeller trim calculations.
📝 Worked Example
Pump at 1750 RPM: Q=500 GPM, H=120 ft, P=25 HP. New speed: 1200 RPM.
Ratio = 1200/1750 = 0.686 | Q₂ = 500×0.686 = 343 GPM
H₂ = 120×0.686² = 56.5 ft | P₂ = 25×0.686³ = 8.06 HP
343 GPM | 56.5 ft head | 8.06 HP — 67.8% power saving!