Drawing No. EH–FM–020 // Fluid Mechanics & Piping
Pump Efficiency Calculator
Reviewed August 2026
Work through the full power chain from electrical input to hydraulic output — hydraulic power, shaft (brake) power, pump efficiency, and overall wire-to-water efficiency including the motor.
What problem does this solve?
A pump's efficiency tells you how much of the energy going into it actually ends up moving fluid, versus being lost to friction, turbulence and mechanical losses inside the pump — directly setting its energy cost over years of operation. This tool works through the full chain from hydraulic (useful) power up through shaft power to electrical input power, so you can see exactly where the losses are happening: inside the pump itself, or in the motor driving it.
Inputs
Results
Background
Phydraulic = ρgQH, the actual useful power delivered to the fluid — the rate of doing work lifting and pressurizing the flow against the system's total head. This is the power a perfectly efficient pump would need; any real pump needs more shaft power than this to overcome internal losses.
ηpump = Phydraulic/Pshaft, the fraction of shaft power that actually becomes useful hydraulic power. The rest is lost to internal fluid friction, turbulence (recirculation and shock losses at off-design flow), mechanical friction in bearings and seals, and leakage recirculation inside the pump. Well-designed centrifugal pumps at their best-efficiency point commonly reach 70–90%, but efficiency falls off well away from that point in either direction.
ηoverall = ηpump × ηmotor = Phydraulic/Pelectrical, the complete chain from electrical input at the motor terminals to useful hydraulic output — the number that actually determines energy cost. A pump might have excellent hydraulic efficiency but be paired with an inefficient or oversized motor, or vice versa; wire-to-water efficiency is the only number that captures the whole system.
A centrifugal pump's efficiency varies continuously along its performance curve — it peaks at the best-efficiency point (BEP) the pump was designed around, and falls off at both higher and lower flow than BEP. Running a pump significantly away from BEP for long periods (a common consequence of oversizing) wastes energy and increases mechanical wear, which is why matching pump selection to the actual expected operating point matters as much as picking a pump that can technically deliver the required head and flow.
Frequently asked questions
Practical questions about inputs, assumptions and interpretation.
That's not physically possible and signals bad input data — most likely the shaft power entered is too low for the stated flow and head, or the flow/head values don't match the actual duty point of the pump you're checking. Double check the shaft power came from the same operating point as the flow and head, ideally read together off the same pump performance curve.
It varies hugely by pump size, type and design point — small pumps (under a few kW) often peak around 40–60% efficiency, while large, well-designed industrial pumps can exceed 85–90% at their best-efficiency point. Positive-displacement pumps behave differently, often maintaining relatively flat, high efficiency across a wider flow range than centrifugal pumps.
Because the electricity bill is paid for electrical input power, not hydraulic output — a pump with 85% hydraulic efficiency driven by a poorly matched or partially-loaded 88% efficient motor delivers meaningfully less overall efficiency (about 75%) than the pump efficiency alone would suggest, directly affecting real operating cost.
Manufacturer pump curves typically publish shaft (brake) power directly as a function of flow rate for each impeller size — read the shaft power at your actual flow rate off the curve. If only motor electrical input is known, this calculator's wire-to-water mode lets you work from that instead, though it can't separate pump efficiency from motor efficiency without also knowing one of them independently.