Pump Power Calculator

How to use the Pump Power Calculator

1. 1Enter flow, head, liquid density and efficiency.
2. 2Pick the units or options from the menus if the pump power tool offers them.
3. 3Read the pump power in the large result box.
4. 4Look at the extra rows for related figures.
5. 5Press Copy result to keep the answer.

When you need the pump power

Homeowners sizing a well or garden pump, engineers and students use it.

Head is the vertical lift plus losses from friction in pipes and fittings. Efficiency of small pumps is often only 40 to 60 percent, while large ones can exceed 80 percent.

How the pump power is worked out

Hydraulic power = density × 9.80665 × flow × head. Shaft power = hydraulic power ÷ efficiency. Flow is in cubic metres per second. Pumping 10 litres per second of water against a head of 30 m needs 2,942 W of hydraulic power. At 65% efficiency, the shaft power is 4,526 W, or 6.07 hp.

Every answer on this page comes from that one rule, so you can check any result by hand with a calculator. The figures shown underneath, such as other units, are conversions of the same answer.

• Watts and horsepower
• Energy per hour
• Any liquid density

Mistakes to avoid with pump power

Add a safety margin of 10 to 20 percent to the motor size. Watch that flow is in litres per second, not per minute. Thick liquids need more power.

On phone and computer

On a phone, type into the boxes one after another and read the pump power underneath; Copy result puts it on the clipboard for a message or a note. On a computer the inputs sit on the left and the answer on the right, so you can change one figure and watch the pump power move. The pump power calculator works the same on both.

Checking your pump power by hand

A good habit is to test the pump power calculator with a case you already know. Pumping 10 litres per second of water against a head of 30 m needs 2,942 W of hydraulic power. At 65% efficiency, the shaft power is 4,526 W, or 6.07 hp.

If your own figures give a surprising answer, repeat the working yourself: Hydraulic power = density × 9.80665 × flow × head. Shaft power = hydraulic power ÷ efficiency. Flow is in cubic metres per second. Small differences usually come from rounding, from mixing units, or from a typing slip in one of the inputs. Pump power depends on the flow and pressure, so check those first. Use the Pipe Flow Calculator for flow, the Pressure Converter for units, and the Wind Turbine Power Calculator to compare another fluid-driven machine.

Features

• Flow in litres per second
• Add a motor margin
• Friction counts in the head
• Clear messages when the pump power inputs make no sense
• Copy the result with one tap
• Private: nothing is uploaded

Frequently asked questions