Irrigation Pump Selection Calculator

Calculate required pump horsepower from total dynamic head and flow rate using Hazen-Williams friction loss.

Inputs

Required flow (GPM)

Static lift (ft)

Operating pressure (PSI)

Pipe length (ft)

Pipe diameter (in)

Hazen-Williams C

Pump efficiency (%)

Energy cost ($/kWh)

Annual run hours

Tab to move between fields

Results

Total Dynamic Head (ft)

112.4

Recommended motor (HP)

Friction loss (ft)0

Water horsepower1.42

Brake horsepower2.03

Pipe velocity (ft/s)2.27

Annual energy cost ($)$272.00

How to Use This Calculator

Enter required flow rate in GPM and static lift in feet from source to highest point.
Set operating pressure in PSI at the sprinkler or emitter and mainline pipe length in feet.
Enter pipe diameter in inches and Hazen-Williams C factor for your pipe material.
Set pump efficiency (%) and annual run hours for energy cost estimation.
Review Total Dynamic Head (ft), Recommended motor (HP), and Annual energy cost ($) to select the right pump.

How the result changes with Operating pressure (PSI)

Operating pressure (PSI)	Total Dynamic Head (ft)	Recommended motor (HP)
20	66.2	1.5
70	181.7	5
130	320.3	7.5
180	435.8	10

What each input means

Required flow (GPM): Total system flow rate needed in gallons per minute.
Static lift (ft): Vertical distance water must be lifted from source to highest point.
Operating pressure (PSI): Required pressure at the sprinkler head or emitter.
Pipe length (ft): Total length of mainline pipe.
Pipe diameter (in): Inside diameter of mainline pipe in inches.
Hazen-Williams C: Pipe roughness coefficient. PVC=150, new steel=140, old steel=100.
Pump efficiency (%): Pump efficiency at operating point. Typical: 60-80%.
Energy cost ($/kWh): Electricity cost per kilowatt-hour.
Annual run hours: Expected pump operating hours per year.

What each result means

Total Dynamic Head (ft): Sum of static lift, operating head, and friction loss.
Friction loss (ft): Pipe friction loss via Hazen-Williams equation.
Water horsepower: Theoretical power needed to move water (WHP = GPM x TDH / 3960).
Brake horsepower: Actual shaft power required accounting for pump efficiency.
Recommended motor (HP): Next standard motor size above brake HP.
Pipe velocity (ft/s): Water velocity in mainline. Ideal range: 3-7 ft/s.
Annual energy cost ($): Estimated yearly electricity cost for pump operation.

How this is calculated

Worked example, using the default values

Identify Input Parameters
4 parameters
Required flow (GPM) = 50, Static lift (ft) = 20, Operating pressure (PSI) = 40, Pipe length (ft) = 500 = 9 input(s) provided
Calculate Total Dynamic Head
Total Dynamic Head = staticLiftFt + operatingHeadFt + totalFrictionLoss
112.4 = 112.4
Calculate Recommended motor
Recommended motor
3 = 3
Calculate Friction loss
Friction loss = frictionPer100 * (pipeLength / 100)
0 = 0
Calculate Water horsepower
Water horsepower = (flowGPM * tdh) / 3960
1.42 = 1.42

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