Well & Irrigation Pump Sizing Calculator
Enter the flow you need, the height you must lift water, your pipe run and the pressure you want at the outlet. The calculator returns total dynamic head, brake horsepower, the next standard motor size and what the pump costs to run.
Works for submersible, jet and irrigation pumps · No signup · Runs entirely in your browser
Describe the job
Use the pumping water level, not the drilled depth, and the peak flow you need.
Friction uses the Hazen-Williams formula with C = 140 for PVC or poly pipe. If your pump data gives one wire-to-water efficiency instead of separate pump and motor figures, enter it as pump efficiency and set motor efficiency to 100.
Where the head goes
155.3 ft total dynamic head
How to use the pump sizing calculator
- Measure the pumping water level. The vertical lift is the distance from the water surface while the pump runs, not the depth of the well. If you only know the static level, subtract the expected drawdown.
- Set the peak flow. A typical house needs 5–10 GPM. Add irrigation zones, stock tanks, heat pumps and simultaneous fixtures. Size for the busiest hour, not the daily average.
- Set the pressure. A household pressure switch usually targets 30–50 PSI; irrigation and some filtration systems want 40–60 PSI. Pressure at the outlet becomes extra head whether the water is moving or not.
- Enter the pipe run and diameter. Friction grows with length and falls steeply as diameter increases. Include the drop pipe in the well as well as the horizontal line.
- Check the duty point against a pump curve. The result is the flow and head a pump must produce. Pick a pump whose published curve passes through that point near its best efficiency range.
Lift is not the same as well depth
A 300-foot well does not need a pump rated for 300 feet of head if the water sits at 40 feet. What matters is the pumping water level: how far the water surface falls below the discharge point while the pump is running. A pump that is sized from drilled depth is oversized, throttled by a pressure tank or cycle, and more expensive to run.
Static level is the level with the pump off. Drawdown is the drop caused by pumping. Pumping level is the two combined. A well report may list all three. If you do not know the drawdown, adding 10–20 feet of margin is cheaper than replacing a pump that runs dry.
The formulas behind the result
- Pressure head: PSI × 2.309 = feet of head. Forty PSI is about 92.4 feet.
- Friction head: Hazen-Williams at C = 140 for PVC/poly, plus the fittings allowance. The full pipe run, including the drop pipe, is used.
- Total dynamic head (TDH): lift + pressure head + friction head.
- Water horsepower: GPM × TDH ÷ 3960.
- Brake horsepower: water horsepower ÷ pump efficiency.
- Motor input: brake horsepower ÷ motor efficiency, then × 0.7457 for kW.
The recommended motor is the next standard size above the calculated motor input. Standard sizes jump from 0.75 to 1, 1.5, 2, 3, 5, 7.5, 10 and beyond, so a calculated 0.77 HP becomes a 1 HP motor.
Which pump type fits the lift?
Shallow-well jet pumps can lift water roughly 25 feet or less because they rely on suction. Above that, use a deep-well jet or, more commonly, a submersible pump lowered into the well. Deep submersibles typically run on 240 volts and need a control box, pressure switch, check valve and dry-run protection. Turbine pumps serve high-flow irrigation and municipal wells.
Horsepower is only one part of the choice. A pump also has a maximum flow, a shutoff head and a best-efficiency range. Compare the whole curve at your duty point, not just the motor nameplate.
Pipe friction reference
Head loss in feet per 100 feet of pipe at C = 140, before the fittings allowance:
| Flow (GPM) | 1 in | 1.25 in | 1.5 in | 2 in |
|---|---|---|---|---|
| 5 | 2.20 ft | 0.74 ft | 0.31 ft | 0.08 ft |
| 10 | 7.94 ft | 2.68 ft | 1.10 ft | 0.27 ft |
| 15 | 16.83 ft | 5.68 ft | 2.34 ft | 0.58 ft |
| 20 | 28.68 ft | 9.67 ft | 3.98 ft | 0.98 ft |
Galvanized pipe and older steel pipe have rougher walls and lose more head; copper and new plastic are closer to the table. Elbows, tees, valves and a check valve add the fittings allowance.
What this calculator does not cover
- The pump curve. A motor size is not a pump selection. Verify the chosen pump delivers your flow at your head without running far out on its curve.
- Well yield. If the well produces less than the pump demands, the pumping level drops and the pump can run dry. Test yield before sizing.
- Wire voltage drop. Long runs and undersized cable reduce voltage at a submersible motor and shorten its life.
- Pressure tanks and controls. Tank size, precharge, pressure switch settings and cycle stop valves affect run time and cost.
- NPSH, altitude, temperature and variable-speed drives. These need the pump manufacturer's data and a site-specific design.
This is a planning estimate, not a substitute for a licensed well contractor or a pump manufacturer's selection software. Confirm the final pump, motor, wire and controls against local code.
Frequently asked questions
What size pump do I need for my well?
Size from the flow you need and the total dynamic head it must overcome, then choose a pump whose published curve delivers that duty point at good efficiency. A typical house needs 5 to 10 GPM at 30 to 60 PSI; irrigation and stock watering usually need more. This calculator gives you the head and horsepower to compare against a pump curve.
How do I calculate pump horsepower?
Brake horsepower equals flow in GPM multiplied by total dynamic head in feet, divided by 3960 and then by pump efficiency. For example, 10 GPM against 155 feet of head at 60 percent efficiency needs about 0.65 brake horsepower, so the next standard motor is 1 HP.
What is total dynamic head?
Total dynamic head is the sum of the vertical lift from the pumping water level, the pressure head needed at the outlet, and the friction loss through pipe and fittings. It is measured in feet of water; one PSI equals about 2.31 feet of head.
Should I use well depth or water level?
Use the pumping water level, not the drilled depth. The water level can drop while the pump runs, so measure the static level and subtract the drawdown, or use the level a nearby well report records under pumping. Drilled depth overstates the lift and oversizes the pump.
How many GPM does a house need?
Most homes are served by 5 to 10 GPM. Add demand for irrigation zones, heat pumps, filling a stock tank or running several fixtures at once. The well must also be able to sustain that flow; a pump cannot deliver more water than the well yields.
Does pipe size affect pump size?
Yes. Friction rises sharply as pipe diameter falls and flow rises. At 10 GPM, one-inch pipe loses about 7.9 feet of head per 100 feet, 1.25-inch about 2.7 feet, and two-inch about 0.3 feet. A long run of undersized pipe can add more head than the lift itself.
How much does it cost to run a well pump?
Multiply motor input power in kW by run hours and your electricity rate. The default example, 10 GPM against 155 feet of head for two hours a day at 16 cents per kWh, uses about 1.15 kWh a day and costs roughly $5.51 a month. Actual run time depends on demand and pressure-tank settings.