Pump Sizing Calculator
Size a centrifugal pump: hydraulic power, brake power and motor kW from flow, head and efficiency.
Inputs
1.0 for water at 60°F.
Results
Flow (metric)22.71m³/h
Head (metric)36.58m
Hydraulic power3.03HP
Brake power4.33HP
Brake power3.23kW
Motor input power3.51kW
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Formula
Brake HP = (Q × H × SG) / (3960 × η_pump); Motor kW = Brake HP × 0.7457 / η_motor
Worked example
100 GPM @ 120 ft TDH, SG 1.0, 70% pump / 92% motor → Hyd HP 3.03, Brake HP 4.33, Motor kW ≈ 3.5 kW.
Frequently asked questions
Where does the constant 3960 come from?
3960 = 33,000 ft·lb/min per HP ÷ 8.33 lb/gal (water). Q × H × SG / 3960 gives water HP directly in imperial units.
What pump efficiency should I use?
50–65% for small end-suction pumps, 65–80% for mid-size ANSI, up to 85% for large split-case. Use manufacturer curve when available.
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