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Water Pump Sizing Calculator

Pump sizing from flow and head. Friction head is what undersized pipe adds, and it rises with the square of velocity, so a bore one size up often saves more energy than a better pump.

Also called: pump head calculator, pump hp calculator.

litres/min
m
m
mm
%
Total head
14.37

14.37 m of total head: 12 m of lift plus 2.37 m of friction. That needs 140.87 W of hydraulic power, or 0.24 kW at 60% efficiency, which is 0.32 hp. Velocity in the pipe is 1.24 m/s. Velocity is within the usual range, so friction losses are reasonable.

Friction head
2.37
Hydraulic power
140.87
Motor power
0.24
In horsepower
0.32
Pipe velocity
1.24
Equivalent pipe length
48
On friction losses
Velocity is within the usual range, so friction losses are reasonable.
How this is calculated
Method and background

How this is calculated

Total head is the vertical lift plus friction losses in the pipe and fittings. Friction depends on velocity squared, so halving the pipe area roughly quadruples the loss. That is why pipe sizing matters as much as pump selection: a system with a long run of undersized pipe spends most of its energy on friction rather than on lifting water. Velocity above about 2 m/s is a sign the pipe is too small, and it causes noise and erosion as well as loss.

total head is static lift plus friction, and friction rises with the square of velocity
Q
Flow rate
H
Total head
eta
Efficiency

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

60 litres a minute lifted 12 metres

Flow required
60 litres/min
Vertical lift
12 m
Pipe run
40 m
Pipe bore
32 mm
Bends and fittings
8
Pump efficiency
60%

Total head14.37

0.001 m3/s over the 32 mm bore area

Open this example

no friction leaves only the lift

Flow required
60 litres/min
Vertical lift
12 m
Pipe run
0 m
Pipe bore
32 mm
Bends and fittings
0
Pump efficiency
60%

Total head12

boundary

Open this example

Method and limits

What it assumes

  • Water at ambient temperature in a reasonably smooth pipe.

What it deliberately does not model

  • Uses a simplified friction factor rather than a full Darcy-Weisbach iteration.
  • Suction lift is limited by atmospheric pressure to about 7 metres in practice.
  • Pump curves are not linear, so the operating point depends on the specific pump.

Formula version 1.0.0 · definition 1.0.0 · India · Report a problem with this calculator

Frequently asked questions

Why does my pump not deliver its rated flow?
Rated flow is at a stated head. Friction in the pipework adds to the lift, and a pump on a long run of narrow pipe operates much further along its curve than the rating suggests.
Is a bigger pipe worth it?
Often more than a bigger pump. Friction rises with velocity squared, so one size up on the bore can cut the friction head substantially and let a smaller motor do the job.