Pump Brake Horsepower
Also known as BHP · shaft horsepower · motor size for a pump
Worked example: 90 m3/h at 60 m absorbing 19.6133 kW → eta = 0.75 — press Try an example to run it live, then adjust anything.
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Shaft power and efficiency →
UniversityFluid Mechanics, HVAC & Refrigeration
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Pump Brake Horsepower explained
Brake horsepower is water horsepower divided by the pump's efficiency — the power that actually shows up on the coupling, and therefore the number that sizes the motor. Take 500 gpm at 100 ft on water through a 70%-efficient pump: 500 × 100 × 1.0 / (3960 × 0.70) ≈ 18.0 hp, so a 20 hp motor. The 3960 is the same US-customary constant as in water horsepower, and this page evaluates the exact SI equivalent ρgQH/η so you may enter L/s, metres and kilowatts freely.
Efficiency is not a property of the pump; it is a property of the operating point. A pump rated 78% at best efficiency may run at 55% out on the far right of its curve, and the shaft power can then exceed the nameplate even though the flow looks reasonable. Read η off the curve at your actual duty, not off the datasheet headline, and add the motor's own efficiency (typically 90–94%) if you want electrical input rather than shaft power.
Pump Brake Horsepower formula
- = Brake horsepower (W)
- = Flow rate (L/min)
- = Total head (m)
- = Specific gravity
- = Pump efficiency
Missing one of these? Work it out first, then come back
- Brake horsepower — Pump Water Horsepower, Fan Brake Horsepower
- Flow rate — Pump Water Horsepower, Hazen–Williams Head Loss
- Total head — Pump Water Horsepower, Hydraulic Power (P = ρgQh)
- Specific gravity — Pump Water Horsepower, Valve Flow Coefficient (Cv)
- Pump efficiency — Pump Efficiency from Hydraulic and Shaft Power, Fan Brake Horsepower