Pump Power Calculator

Hydraulic (useful) power is P_h = ρ·g·Q·H, where ρ is the fluid density, g gravity, Q the flow, and H the total head. In practical form, P_h [kW] = Q[m³/h]·H[m]·relative density / 367. Shaft power (what the motor must deliver) is higher: divide the hydraulic power by the pump efficiency. The calculator does both and also suggests the motor power with a safety margin.

Hydraulic power is the useful energy actually delivered to the fluid. Shaft power (BHP, brake horsepower) is what the pump shaft must receive — always higher than hydraulic, because no pump is 100% efficient: BHP = hydraulic / efficiency. Motor power is the shaft power plus a margin (service factor), so the motor never runs at its limit. The calculator shows all three, in kW, CV and HP.

Efficiency (η) is the fraction of shaft power that becomes useful energy in the fluid — the rest turns into heat and friction. In centrifugal pumps it is typically between 60% and 85%, peaking at the best-efficiency point (BEP) of the curve. The higher the efficiency, the lower the shaft power for the same flow and head — and the lower the energy bill. FB Bombas FBCN centrifugal pumps operate at 74% to 86% efficiency at BEP (catalog figure).

Good practice adds a service factor over shaft power so the motor does not run at its limit: typical margins are between 10% and 25%, rounding up to the next commercial motor rating. For non-overloading (rising) power curves a smaller margin suffices; for duty points that may migrate along the curve, use a larger margin. The calculator uses 15% by default and lets you adjust it. Always confirm against the real pump curve at the operating point.

Pump power appears in three units. The kW is the SI unit. The CV (metric horsepower) is the commercial unit of Brazilian and European catalogs: 1 CV = 735.49875 W, so CV = kW × 1.35962. The HP (mechanical horsepower, used in US catalogs) is 1 HP = 745.69987 W, so HP = kW × 1.34102. CV and HP are not equal — the CV is about 1.4% smaller. The calculator shows all three simultaneously.

Yes, directly. Hydraulic power is proportional to density: pumping a fluid denser than water (a brine, for example) requires more power for the same flow and head; a lighter oil requires less. That is why the calculator asks for the water temperature (which adjusts density automatically) or the informed density for other fluids. Note: head in meters of column is already independent of density — what density scales is the energy per meter.