It is tempting to compare pumps by their motor power. A 0.75kW pump sounds like it should move more water than a 0.55kW one, and a 1.5kW pump sounds stronger still. Power is an easy number to read off a box, so it gets used as a shortcut for performance. The problem is that it is a poor one. Two pumps with exactly the same kW rating can move very different amounts of water to very different heights, and understanding why will save you from buying on the wrong number.
kW is what the pump consumes
The first thing to be clear about is what the kW figure actually describes. The motor rating is the electrical power the pump draws, the energy going in. It is not a measure of the water work coming out. Between the electricity going in and the water moving out sits the pump's efficiency, and that varies enormously from one design to another. A well-designed pump turns more of its input power into water movement; a cheaper or poorly matched one wastes more as heat and noise. Same power in, different result out.
What actually decides how a pump performs
Several things matter far more than the headline kW, and they are where good pumps separate from cheap ones.
This is also why pump type matters. A peripheral pump and a centrifugal pump of the same kW are built for different things, one for pressure and one for flow, so comparing their power tells you almost nothing. We explain how impellers turn power into water movement in our guide to how submersible pumps work.
Compare the duty point, not the motor
The best way to compare two pumps is at the duty point you actually need: the flow you require at the head your installation imposes. Read each pump's curve at that head and see which delivers the flow, then look at how hard each is working to do it. A pump running near the efficient part of its curve will move your water for less energy and less wear than one straining at the end of its range, even if they share a kW figure. Our guide to reading a pump curve walks through finding that point, and the deeper trap of trusting the top number is covered in why max flow is not your real flow.
The practical takeaway
A bigger motor is not a better pump, and a smaller kW figure can outperform a larger one if the pump is better designed for the job. Buy on flow and head at your duty point, on efficiency, and on build quality, not on the power label. If you want help comparing two pumps fairly, send us the duty you need and the models you are weighing up, and we will read the curves with you.
Frequently asked questions
Does a higher kW pump always move more water?
No. The kW rating is the power the motor draws, not the water it delivers. A higher efficiency pump, or one with an impeller better suited to the job, can move more water than a higher kW pump that is less efficient or designed for a different duty. Compare flow and head at your duty point rather than motor power.
What should I compare instead of kW?
Compare the flow each pump delivers at the head your installation imposes, which is the duty point, along with the pump's efficiency and build quality. Reading each pump's performance curve at your required head tells you far more than the motor rating does.
Why do two pumps with the same power cost different amounts?
Usually because of efficiency, materials and build quality. A dearer pump often turns more of its power into water movement, uses better bearings, seals and materials, and holds its performance for longer. The motor rating being equal, those differences are what you are paying for and what determine real performance over time.
Is a peripheral pump comparable to a centrifugal pump of the same kW?
Not directly, because they are built for different things. A peripheral pump produces high pressure and modest flow, while a centrifugal pump produces more flow at lower pressure. Two pumps of the same kW but different type will perform very differently, so the comparison has to be made on flow and head for the job, not on power.
