Water Pump HP Calculator
Find the pump horsepower needed to lift water to your tank from the flow rate, total height and pipe losses.
Inputs
Sump level to tank inlet
Formula
- Total head = static lift + friction loss (≈5% of pipe length)
- Hydraulic power (kW) = ρ × g × Q × H ÷ 1000
- Motor HP = power ÷ efficiency ÷ 0.746
A pump has to lift the water (static head) and push it through the pipe (friction head). Together these give the total head. Power is simply weight of water per second times height, divided by how efficient the pump is. Small domestic pumps are 45–60% efficient, so the motor is always bigger than the pure hydraulic power.
Step-by-step calculation
- 1
Head
static + friction
13.25 m
- 2
Power
ρ g Q H / 1000
0.13 kW
- 3
Motor HP
kW ÷ efficiency ÷ 0.746
0.32 HP
Worked example
- 160 litres/min to a tank 12 m above the sump through 25 m of pipe.
- 2Friction adds about 1.25 m → total head 13.25 m.
- 3Power = 1000 × 9.81 × 0.001 × 13.25 ÷ 1000 = 0.13 kW; at 55% and 0.746 → 0.32 HP, so a 0.5 HP pump is chosen.
Tips
- Always round up to the next standard pump: 0.5, 1, 1.5, 2, 3 HP.
- Use one pipe size larger than the pump outlet on long runs — friction drops sharply.
Frequently asked questions
What pump HP do I need for a 2-storey house?
A 0.5 HP pump handles most 2-storey homes; 1 HP is common for 3 storeys or long pipe runs.
Does a bigger pump fill the tank faster?
Yes, but it also draws more current and can suck the sump dry. Match the pump to the tank size and source yield.
What is head?
The vertical height the water must be lifted, plus an allowance for pipe friction — both measured in metres.
Related calculators
Keep going with more engineering tools.
Pump Flow Rate Calculator
Convert a pump's flow between litres per minute, litres per hour, m³/h and gallons, and see how long a tank takes to fill.
Tank Filling Time Calculator
Find out how long your pump takes to fill a water tank, and the electricity it uses each time.
Pipe Size Calculator
Choose the right pipe diameter for a given water flow so the velocity stays safe and pressure loss is low.
Borewell Water Yield Calculator
Measure your borewell's yield in litres per hour from a simple bucket test, and see how many homes it can supply.
Pipe Volume Calculator
Calculate how many litres of water a pipe holds and how long it takes to flush or fill it.
Air Compressor Calculator
Check whether your air compressor's tank and CFM match your tools, and how long the tank takes to refill.