Pump Size Calculator
Enter the flow you need, the height the water must be lifted, the length and bore of the pipe and the pump efficiency. The calculator gives the total head, the power needed and a motor size.
- Total dynamic head
- Friction included
- Motor size in kW
For clean water. Efficiency is usually 40% to 60% for small pumps and up to 80% for large ones.
A pump is chosen by flow and head together. Head is the height the pump can push water, plus the extra lost to friction in the pipes. A pump that delivers 100 litres a minute at 5 m might only manage 40 at 20 m. You need a pump whose curve passes through your flow at your total head.
Pump power chart
Shaft power at 55% efficiency. Search for a flow or head.
| Flow (L/min) | 10 m head | 20 m head | 40 m head | 60 m head |
|---|---|---|---|---|
| 50 | 0.15 | 0.3 | 0.59 | 0.89 |
| 100 | 0.3 | 0.59 | 1.19 | 1.78 |
| 200 | 0.59 | 1.19 | 2.38 | 3.57 |
| 400 | 1.19 | 2.38 | 4.76 | 7.13 |
| 800 | 2.38 | 4.76 | 9.51 | 14.3 |
| 1600 | 4.76 | 9.51 | 19 | 28.5 |
Power = flow × head × 9.81 ÷ efficiency. Add 15% or more when choosing the motor so it is not run flat out.
Lift and power
100 L/min at 60% efficiency. Slide the lift.
Friction is shown here as a fixed 1.5 m. On long or narrow pipes it can be bigger than the lift itself.
How to size a pump
Head, then power. Step through it.
Set the flow
What you need at the outlet.
Undersized pipes are the most common reason a pump disappoints. A larger pipe can cut friction head dramatically.
Centrifugal, submersible or booster
Common water pump types. Compare them.
Surface pump for transfer, irrigation and circulation.
Sits in the water and pushes it up. For wells and sumps.
Raises mains or tank pressure for homes and buildings.
Surface pumps can only lift water about 7 m by suction. Deeper water needs a submersible pump in the well or tank.
Before buying a pump
Match the pump to the job. Tick each item.
Tick each item as you go.
Running a pump far from its best efficiency point wastes energy and wears it out. Aim for the middle third of its curve.
What you get
The numbers on a pump datasheet. Each tile explains one result.
Lift plus friction.
Height the water climbs.
Lost in pipe and fittings.
Hydraulic and shaft.
Standard size with margin.
Hydraulic power is the work done on the water. Shaft power is higher because no pump is 100% efficient.
Frequently Asked Questions
No question matches that search.
How do I calculate pump size?
Find total head (lift plus friction), then power = 9.81 × flow (m³/s) × head ÷ efficiency.
What is total dynamic head?
The total height a pump must push water, including friction losses.
What size pump for 100 litres per minute at 12 m?
About 0.4 kW shaft power at 55% efficiency, so a 0.55 kW motor.
How much does pipe size affect a pump?
A lot. Halving the bore can increase friction more than 30 times.
What efficiency should I assume?
40% to 60% for small pumps, up to 80% for large ones.
How high can a surface pump lift by suction?
About 7 m in practice. Deeper water needs a submersible pump.
How do I convert kW to horsepower?
Multiply by 1.341.
A pump that hits the duty point
Work out total head with friction, then find the power for your flow. Choose a pump whose curve passes near your duty point and a motor with margin, and it will run efficiently for years.
More size calculators
Each one has its own calculator, worked examples and answers to common questions.