Pump Power Calculator
Hydraulic power and shaft power from flow, head, and efficiency.
Calculator
No signup required. Results are indicative—verify for your standards.
Hydraulic power: 19.62 kW
Shaft power (approx.): 26.16 kW
Formula
Hydraulic power P_h = ρ × g × Q × H (W). Shaft power P_shaft = P_h / η, with Q in m³/s, H in m, ρ in kg/m³, g = 9.81 m/s², η overall efficiency (0–1).
Example calculation
Water (ρ=1000), Q = 0.05 m³/s, H = 40 m, η = 0.75: P_h ≈ 19.62 kW, P_shaft ≈ 26.2 kW.
Engineering notes
Use total dynamic head including static, friction, and velocity head. η combines hydraulic and motor efficiency; de-rate for service factor.
When to use this calculator
- Motor selection — calculate the minimum motor kW required before specifying a pump driver
- Energy audit — estimate annual electricity consumption for a pumping circuit at known duty hours
- Fire pump sizing — determine hydraulic kW for firefighting pumps per NFPA 20 or IS 12288
- Project costing — include pump motor power in electrical load lists for MCC and transformer sizing
- Feasibility studies — quickly compare alternative pumping heads and flow rates to select the most efficient system
Frequently asked questions
- What is total dynamic head (TDH) and how do I calculate it?
- Total dynamic head is the total energy (in metres of fluid) that the pump must impart to the fluid. TDH = Static head + Friction head + Velocity head + Pressure differential. Static head is the elevation difference between suction and discharge liquid levels. Friction head is the pressure drop due to pipe friction and fittings (calculated with Darcy-Weisbach). Velocity head is usually small and often neglected for preliminary sizing.
- What pump efficiency should I use if I don't have a datasheet?
- For preliminary sizing, use 0.65–0.70 (65–70%) for small pumps under 10 kW, and 0.70–0.80 for larger industrial centrifugal pumps. High-efficiency pumps above 100 kW can reach 85–88%. The motor efficiency (typically 90–95% for IE2/IE3 motors) is separate — the overall efficiency η in this formula combines hydraulic pump efficiency and motor efficiency: η_overall = η_pump × η_motor.
- How do I convert flow rate from m³/h or LPM to m³/s?
- Divide m³/h by 3600 to get m³/s. Divide LPM (litres per minute) by 60,000 to get m³/s. For example, 180 m³/h = 180/3600 = 0.05 m³/s. For US gpm, multiply by 0.0000631 to get m³/s.
- Can this calculator be used for viscous liquids (heavy oil, slurry)?
- The formula is valid for any fluid — use the correct density (ρ) for your fluid. However, for highly viscous fluids (above ~50 cP), the pump efficiency degrades significantly compared to water. Apply viscosity correction factors (per HI 9.6.7 or Hydraulic Institute standards) to de-rate both the head and efficiency from the water-based pump curve.