Hydraulic power
Pₕ = ρgQH
ρ is pumped-liquid density, Q is flow in m³/s and H is total dynamic head.
Existing engineering calculator
Pump Motor Selection Calculator
Calculate hydraulic power, shaft power, motor input power and a preliminary standard motor recommendation from rated flow, head, liquid density, efficiency and design margin.
Calculator inputs and result
Select the pumped liquid, then enter rated flow, total dynamic head, efficiency values and design margin. The liquid density is editable so verified project data can be used.
Liquid density directly affects hydraulic power. Presets are typical values only; use verified operating-condition data for final selection.
Engineering knowledge
Pump power, liquid density, efficiency and motor selection
Pump selection starts with the required flow and total dynamic head. Hydraulic power also depends directly on pumped-liquid density. The calculated hydraulic power must be increased to allow for pump and motor losses, then a practical motor rating is selected with a suitable design margin.
Related calculation knowledge
Total dynamic head must already include static head and all relevant system losses. Use actual density at operating temperature and composition.
Explore Fluid Mechanics and Piping →Formula and inputs
Shaft power
Pₛ = Pₕ / ηₚ
Pump efficiency increases the required shaft power.
Motor selection
Pᵈ = Pₛ / ηₘ × (1 + margin)
The calculator selects the next listed standard motor rating.
Assumptions and limitations
- This is a preliminary steady-state power estimate.
- Presets are typical liquid densities, not material specifications; density can vary with temperature and composition.
- NPSH, viscosity, pump curve, motor service factor, starting method, altitude and site electrical supply are not checked.
- Confirm final selection against manufacturer data, standards and qualified engineering review.
Frequently asked questions
Why does the liquid density matter?
At the same flow and head, a denser liquid needs proportionally more hydraulic power.
Can I use a custom liquid?
Yes. Select the custom option and enter a verified operating density in kg/m³.
Does this select a pump?
No. It estimates a motor size from entered duty conditions; hydraulic suitability still requires a pump-curve review.
Engineering disclaimer
Educational and preliminary engineering-reference use only.Verify liquid properties, pump curve, operating conditions, motor specification and applicable standards before procurement, construction or operation.