Irrigation Pump Power Calculator & kW, HP & Motor Size
Sizes pumps for borewells
Size your pump right — enter flow and total head with pump and motor efficiency to get the kW and HP, a suggested motor size, and the daily energy use and cost.
Typical centrifugal pump 50–70%; electric motor ~85–92%. Head = suction lift + delivery height + pipe friction losses.
To pump 10 L/s against 20 m of head you need about 3.27 kW (4.39 HP) at the pump shaft, drawing roughly 3.63 kW from the supply. Pick the next standard motor up — about 5 HP.
Next: measure total head honestly (lift + delivery + friction) — under-sizing starves the system and over-sizing wastes energy. A more efficient pump and minimising friction losses both cut your running cost.
Estimate from P = ρgQH ÷ efficiency. Real duty depends on the pump curve, pipe friction and operating point — confirm against manufacturer data.
Pump power — key facts
- Hydraulic kW
- 0.00981 × L/s × head (m)
- Shaft power
- hydraulic ÷ pump efficiency
- Input power
- shaft ÷ motor efficiency
- 1 HP
- ≈ 0.7457 kW
- Pump efficiency
- ~50–70%
- Motor efficiency
- ~85–92%
- Total head
- lift + delivery + friction
- Privacy
- Runs in your browser; nothing uploaded
From flow and head to the right motor
A pump's job is to move a flow of water against a head, and the power that takes is fixed physics: hydraulic power = ρ·g·Q·H. For water that simplifies to about 0.00981 × flow in litres per second × head in metres, giving kilowatts. But the motor must supply more than that — divide by the pump efficiency to get the shaft power the impeller needs, and again by the motor efficiency to get the electricity drawn. The tool reports all three and converts to horsepower.
Getting this right saves money twice. Undersize and the pump can't deliver the flow or head, starving your irrigation; oversize and you pay for a bigger motor and waste energy every hour it runs. The tool rounds up to the next standard motor size for a safe margin, and — with running hours and your tariff — shows the daily and monthly energy cost, so you can compare a more efficient pump against its price. Measure total head honestly, including pipe friction, for a sizing you can trust.
Size the motor
Turn flow and head into the kW/HP needed and the next standard motor size to buy.
Avoid over/under-sizing
Match the pump to real duty so you neither starve the system nor waste energy.
Estimate running cost
See daily and monthly energy use and cost from your hours and electricity tariff.
Compare pumps
Test how pump efficiency changes power and cost to justify a better pump.
Frequently Asked Questions
How do I calculate pump power?+
Hydraulic power (kW) = ρ·g·Q·H ÷ 1000, which with water works out to 0.00981 × flow (L/s) × head (m). Divide by the pump efficiency for shaft power, and by the motor efficiency for the electrical input. This tool does all three and converts to HP.
What HP pump do I need?+
It depends on flow and total head, not just one of them. For example, 10 L/s against 20 m of head at 60% pump efficiency needs about 3.3 kW (4.4 HP) at the shaft. Enter your figures and the tool suggests the next standard motor size up.
What is total head?+
Total head is the total resistance the pump works against, in metres: the suction lift from the water level to the pump, plus the delivery height to the outlet, plus friction losses in the pipes and fittings. Underestimating friction is the most common sizing mistake.
What pump and motor efficiency should I use?+
Centrifugal irrigation pumps are typically 50–70% efficient; submersibles vary. Electric motors are usually 85–92%. Use the manufacturer's figures if you have them — lower efficiency means a bigger motor and higher running cost for the same water.
How do I convert kW to HP?+
One metric/mechanical horsepower is about 0.7457 kW, so divide kW by 0.7457 to get HP (or multiply HP by 0.7457 for kW). The tool shows both shaft and input power in kW and HP so you can match a motor rating.
Why size the motor above the requirement?+
Motors come in standard sizes and should run comfortably below their rating, with margin for a clogged filter, worn pump or higher-than-expected head. The tool rounds the input power up to the next common motor size so the pump isn't overloaded.
How do I work out running cost?+
Multiply the motor input power (kW) by the hours run per day for the daily energy in kWh, then by your electricity tariff for the cost. Add running hours and price in the tool to see daily and monthly energy cost.
Does a bigger pump give more water?+
Only up to what the pump curve and pipe allow at the operating head — oversizing wastes energy and can damage the system, while undersizing fails to deliver the flow or head. Match the pump to the actual flow and head your irrigation needs, which this tool quantifies.
Can I enter flow in m³/h?+
Yes — switch the flow unit to m³/h and the tool converts internally (1 L/s = 3.6 m³/h). Use whichever your pump or design specifies.
Is this exact for my pump?+
It's an accurate power requirement from physics, but the real duty point depends on the pump's performance curve and the system's pipe friction. Use it to size the motor and estimate energy, then confirm against the manufacturer's curve.