Pump Calculator
Calculate hydraulic power, shaft power and motor power for your pump system. Enter flow rate, head, specific gravity and efficiency to size your pump correctly.
How the pump calculator works
This calculator determines the hydraulic power delivered to the fluid, the shaft power required at the pump shaft, and the motor power needed to drive the pump. It uses the fundamental pump power equation: Hydraulic Power (kW) = (Flow × Head × Specific Gravity × 9.81) / 1000, where flow is in m³/h and head is in meters.
Enter the flow rate, total head, specific gravity of your fluid, pump efficiency and motor efficiency. The calculator instantly shows the hydraulic power, shaft power, motor power, discharge pressure and recommended motor size. Use the activity-level style comparison table to see how different efficiencies affect power requirements.
Step 1: Pump Parameters
Understanding Pump Power
Hydraulic power is the useful power transferred to the fluid. Shaft power includes mechanical losses in the pump. Motor power accounts for electrical and mechanical losses in the motor. Always select a motor with a margin above the calculated value.
Step 2: Efficiency & Settings
Efficiency Guidelines
Typical pump efficiencies range from 40% for small pumps to over 90% for large, well-designed pumps. Motor efficiencies are typically 85–95% for standard induction motors. Higher efficiency reduces operating costs.
Pump Power Results
Required Motor Power
Efficiency Comparison
| Pump Efficiency | Motor Efficiency | Shaft Power (kW) | Motor Power (kW) | Recommended Motor |
|---|
Power Breakdown
Pump Power Calculation Formula
Hydraulic Power = (Q × H × SG × 9.81) / 1000
Where Q = flow rate (m³/h), H = total head (m), SG = specific gravity. Shaft Power = Hydraulic Power / Pump Efficiency. Motor Power = Shaft Power / Motor Efficiency.
Frequently Asked Questions
What is hydraulic power in a pump?
Hydraulic power is the useful power transferred to the fluid by the pump. It is calculated as: Hydraulic Power (kW) = (Flow × Head × Specific Gravity × 9.81) / 1000, where flow is in m³/h and head is in meters.
What is shaft power?
Shaft power is the mechanical power delivered to the pump shaft. It equals the hydraulic power divided by the pump efficiency. It represents the actual power the pump requires to operate.
What is the difference between hydraulic power and shaft power?
Hydraulic power is the power transferred to the fluid, while shaft power is the mechanical power input to the pump. Shaft power is always greater than hydraulic power due to losses in the pump, and the ratio is the pump efficiency.
How do I select the right motor power for a pump?
Motor power is calculated by dividing the shaft power by the motor efficiency. Always select a motor with a power rating higher than the calculated motor power to account for starting torque, voltage variations and other factors — typically 10-15% above the calculated value.
What is specific gravity and why is it important?
Specific gravity is the ratio of the fluid’s density to the density of water. It affects the pressure and power requirements of the pump. For water, specific gravity is 1.0; for heavier fluids like brine (1.2) or lighter fluids like oil (0.85), the power requirement changes proportionally.
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