Pump Power Calculator
Convert flow rate and total head into hydraulic power, pump brake (shaft) power, and motor input power — with pump and motor efficiency, and specific gravity for any liquid.
Duty Point Inputs
Formula
Hydraulic power is the useful work done on the fluid. Brake power accounts for pump hydraulic and mechanical losses (impeller, bearing, seal). Motor input power adds motor and, if applicable, VFD/drive losses — this is the number to size the electrical supply and motor nameplate against.
Worked example
Centrifugal pump: 100 m³/h of water (SG 1.0) at 40 m head, pump efficiency 72%, motor efficiency 93%.
| Step | Calculation |
|---|---|
| Q | 100 m³/h = 0.02778 m³/s |
| Hydraulic power Ph | 1000 × 9.81 × 0.02778 × 40 / 1000 = 10.90 kW |
| Brake power Pb | 10.90 / 0.72 = 15.13 kW (20.29 hp) |
| Motor input power Pm | 15.13 / 0.93 = 16.27 kW (21.82 hp) |
A standard 18.5 kW (25 hp) motor would be selected here, giving roughly 12% service margin above the calculated input power — check against your plant's motor sizing margin standard (commonly 10–20%).
Frequently asked questions
What's the difference between hydraulic power, brake power and motor power?
Hydraulic power is the ideal work delivered to the fluid. Brake power is what the pump shaft actually needs, once pump internal losses are included — it's always higher than hydraulic power. Motor power is what the electrical supply must deliver, once motor (and drive, if used) losses are added on top of brake power.
What pump efficiency should I assume if I don't have a curve?
Small end-suction centrifugal pumps typically run 50–70% efficient; larger, well-matched centrifugal pumps 70–85%; positive displacement pumps often 85–95%. Always use the manufacturer's certified curve at the actual duty point once one is available — assumed efficiency is only for preliminary sizing.
How do I convert head in kPa or bar to metres?
H(m) = P(kPa) × 101.97 / (1000 × SG), or H(m) = P(bar) × 10197 / (1000 × SG). This calculator does that conversion automatically when you select kPa or bar as the head unit.
Should I include a motor service factor margin?
This calculator gives the calculated duty-point power only. Standard practice adds a margin (commonly 10–20%, or per API 610 sizing tables for centrifugal process pumps) before selecting the nameplate motor rating.