Well Pump Sizing Calculator
Estimate the total dynamic head and horsepower a well pump needs from the water depth, desired house pressure and peak demand.
How it works
TDH = pumping depth + (psi × 2.307) + friction · HP = GPM × TDH ÷ 3960 ÷ efficiency
A well pump must lift water from the pumping level, push it up to the desired house pressure, and overcome friction in the drop pipe and service line. Adding those in feet of head gives the total dynamic head, and the same hydraulic-horsepower formula then sizes the pump. Because the pumping water level drops during heavy use, always size on the pumping level, not the calm static level you measure with the pump off.
Worked example
Water sits 100 ft down while pumping, you want 50 psi (about 115 ft of head), and demand peaks at 10 GPM. Adding a 5% friction allowance (5 ft) gives about 220 ft of total dynamic head. Hydraulic HP is 10 × 220 ÷ 3,960 = 0.56 HP, which at 55% efficiency needs about a 1 HP submersible pump.
Frequently asked questions
How much peak flow does a house need?
A rough guide is one GPM per fixture likely to run at once, so 5–7 GPM for a small home and 10–15 GPM for a larger one with multiple bathrooms and irrigation. Peak demand, not average use, sizes the pump.
What is the difference between static and pumping level?
Static level is where the water rests with the pump off. Pumping (dynamic) level is lower — the water drops as the pump draws it down. Sizing on the static level under-sizes the pump because the real lift is greater.
Why include pressure as head?
The pump not only lifts water to the surface but also charges the pressure tank so faucets have force. Each psi of house pressure equals about 2.31 ft of extra head the pump must produce, so 50 psi adds roughly 115 ft.
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This calculator is for educational purposes. Double-check important results before acting on them.