How it works
Pumps are chosen from a manufacturer's pump curve, which shows the flow delivered at a given total dynamic head (TDH). This calculator gives you the two numbers to look up on that curve.
TDH adds the vertical lift from the pumping water level, any rise to the tank, friction losses, and the pressure you need at the tank (1 psi = 2.31 ft of water).
Don't size a pump above the well's sustainable yield. If demand is higher, storage is usually the answer rather than a bigger pump.
The formula
- Capacity = outlets × 1 gpm; peak = outlets used at once × 3 gpm (Nebraska DWEE worksheet)
- TDH (ft) = pumping level + elevation to tank + friction loss + cut-out psi × 2.31
- Horsepower ≈ gpm × TDH ÷ 3,960 ÷ efficiency
How to use this calculator
- Count water outlets and how many run at once.
- Enter pumping level, elevation to the tank and friction loss.
- Enter your pressure switch cut-out.
- Pick a pump whose curve delivers the target gpm at the calculated TDH, within your well's yield.
Frequently asked questions
Why not just use well depth?
The pump lifts water from the pumping water level, not the bottom of the well. Using total depth overstates the head.
Is the horsepower exact?
No. It uses a typical efficiency. Pump curves already account for real efficiency, so use the curve to choose a model.
Sources
- Nebraska Dept. of Water, Energy & Environment: Water Systems Sizing and Selection: 1 GPM per outlet, 3 GPM per outlet used at once; pressure × 2.31 ft; precharge 2 psi below cut-in
Sources last checked Oct 21, 2026Written and reviewed by the Tapped Out team against the sources above.How we calculate