Pump Power Calculator

Calculator

Formula used

How to use this calculator

1. Select whether you want to use head or pressure rise.
2. Enter the flow rate and choose its unit.
3. Enter fluid density and gravity (defaults suit most cases).
4. Provide head (or pressure rise) and select its unit.
5. Enter pump efficiency, and optionally motor efficiency.
6. Press Calculate to view results above the form.
7. Use Download CSV or Download PDF for reporting.

For best accuracy, use the operating point from the pump curve and measured process conditions.

Example data table

Pump power guide

1) Why pump power matters in sizing

Pump power links the hydraulic duty point to real energy demand. Engineers use it to select motor ratings, set electrical protection, and estimate operating cost. A small error in flow or head can shift required shaft power by several kilowatts in medium systems.

2) Typical ranges you can sanity-check

For clean-water centrifugal pumps, operating head is often 10–80 m, while process pumps may exceed 150 m. Flow spans from a few L/min to hundreds of m³/h. Pump efficiency commonly sits near 50–85%, depending on size and proximity to best efficiency point.

3) Data-driven view of the hydraulic equation

Hydraulic power grows linearly with Q and H. For water (ρ≈1000 kg/m³), each 1 m³/s at 1 m head needs about 9.81 kW of hydraulic power. At 0.01 m³/s and 30 m, hydraulic power is roughly 2.94 kW before efficiency losses.

4) Pressure rise versus head inputs

If you measure differential pressure, use ΔP·Q directly. Converting pressure to head helps compare pumps: H = ΔP/(ρg). For water, 100 kPa corresponds to about 10.2 m of head. For lighter fluids, the same pressure equals a higher head value.

5) Efficiency layers and realistic motor sizing

Shaft power includes pump losses: P_shaft = P_hyd/η_pump. Adding motor efficiency gives electrical input. Example: 3.0 kW hydraulic with 70% pump and 92% motor becomes ~4.66 kW electrical. This supports choosing a standard motor size with margin.

6) Unit handling and conversion notes

This calculator converts common flow units (m³/s, m³/h, L/s, L/min, gpm, cfs) into m³/s internally, and converts head (m, ft) or pressure (Pa, kPa, bar, psi) to consistent SI. Using consistent units reduces mistakes during quick design checks.

7) Interpreting results for operation

If calculated shaft power is close to motor nameplate, consider temperature rise, viscosity, and fouling. Operating far from the best efficiency point can increase vibration and energy use. Re-check the duty point on the pump curve and verify actual system head losses.

8) Practical tips for higher accuracy

Use measured flow and differential pressure when possible, and use density at operating temperature. For slurries or viscous fluids, efficiency often drops and required input rises. If you have variable-speed drive data, compute power at multiple duty points to map a realistic operating envelope.

FAQs

1) What is the difference between hydraulic and shaft power?

Hydraulic power is energy delivered to the fluid. Shaft power is what the pump must receive at the shaft to overcome internal losses, so it is higher than hydraulic power by roughly 1/η_pump.

2) Which input method should I use: head or pressure rise?

Use head when you have pump curve data or total dynamic head. Use pressure rise when you have measured differential pressure across the pump. Both methods are equivalent after unit conversion and density adjustments.

3) Why does density affect head conversion from pressure?

Head is energy per unit weight. For the same pressure rise, lighter fluids need a higher head because each kilogram weighs less. The conversion is H = ΔP/(ρg), so lower ρ increases H.

4) How do I choose a motor rating from the result?

Start with electrical input power if motor efficiency is provided. Then apply a practical margin for service factor and uncertainty. Select the next standard motor size above the calculated requirement, following your site’s derating rules.

5) Does this calculator include piping losses?

No. Enter head or pressure rise that already represents the required duty point, including static lift and friction losses. If you only know pipe geometry, compute system head separately and then use that value here.

6) What if the pump efficiency is unknown?

Use a reasonable estimate based on pump type and size. Small pumps may be 40–65%, while larger centrifugal units often reach 70–85% near the best efficiency point. Update the efficiency once manufacturer data is available.

7) Why can measured power differ from calculated power?

Real systems include recirculation, viscosity effects, wear, and operation away from the best efficiency point. Instrument error and variable density also matter. Use this tool as a solid estimate, then validate with field measurements.