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Pump & Fan Motor Power Calculator
Estimate the shaft power and the recommended electric motor rating for a pump (flow + head) or a fan (flow + pressure).
Pump Motor Power
Shaft power: — kW
Recommended motor (×1.15): — kW
P = ρ·g·Q·H / (η · 3.6·10⁶)
Fan Motor Power
Shaft power: — kW
Recommended motor (×1.15): — kW
P = Q·Δp / (η · 3.6·10⁶)
Sizing notes
These give the hydraulic/aerodynamic shaft power; always apply a service margin (≈15%) and round up to the next standard motor size. Browse our power & speed range and pump & fan motors, or the full electric motors catalogue.
Related tools: Electric Motor Calculator · Energy Savings · Power Factor Correction.
Typical efficiency ranges
| Equipment | Typical η |
|---|---|
| Centrifugal pump | 0.60 – 0.80 |
| Centrifugal/axial fan | 0.60 – 0.75 |
After sizing, choose a DRG Motor from the matching power & speed range.
Frequently asked questions
How is pump motor power calculated?
P (kW) = ρ · g · Q · H / (η · 3.6·10⁶), with flow Q in m³/h, head H in m, density ρ in kg/m³ and pump efficiency η. Then add a service margin and round up to a standard motor.
How is fan motor power calculated?
P (kW) = Q · Δp / (η · 3.6·10⁶), with flow Q in m³/h and pressure Δp in Pa.
What service margin should I add?
Typically about 15% above the shaft power, then choose the next standard motor size (e.g. 5.84 kW → 7.5 kW).
What efficiency should I use?
Use the actual pump/fan curve if available. As a rough guide pumps are ~0.6–0.8 and fans ~0.6–0.75.
Which standard motor sizes exist?
Common IEC ratings: 0.55, 0.75, 1.1, 1.5, 2.2, 3, 4, 5.5, 7.5, 11, 15, 18.5, 22, 30, 37, 45, 55, 75, 90, 110, 132, 160, 200, 250, 315, 355 kW.