Well Pump Sizing Calculator
Match pump horsepower to your well depth, household demand, and desired water pressure — using the real hydraulic engineering formula, not a rule of thumb.
How this calculator works
Total Dynamic Head (TDH) is the sum of everything the pump has to overcome: the vertical lift from the water level to the highest fixture, friction loss through the piping, and the pressure you want delivered (converted to feet of head at roughly 2.31 feet per PSI). Water horsepower is then TDH × GPM ÷ 3960 — a standard hydraulics constant derived from water's weight and the definition of horsepower. Because real pumps aren't 100% efficient, we divide by a typical submersible efficiency (~55%) to estimate the actual motor size needed, then round up to the nearest standard size (½, ¾, 1, 1.5, 2, 3 HP).
Where this comes from
This is standard hydraulic pump-sizing engineering, not a niche extension source: TDH and water horsepower formulas are the same math used across the pump industry (Goulds, Grundfos, Franklin Electric) to size submersible well pumps.
Well yield matters too — a pump sized for 10 GPM is useless if your well can only recharge 4 GPM. Have your well's actual recovery rate tested before buying a pump, especially on an older or unfamiliar well.
Frequently asked questions
Why does well depth matter so much for pump sizing?
A pump has to lift water the full vertical distance from the water level in the well up to the point of use, and that lift (along with friction loss) is real work the pump motor has to overcome — a deeper well requires more pump capacity to deliver the same flow and pressure at the surface.
Why is this based on a real hydraulic formula instead of a rule of thumb?
Well depth, household demand, and desired pressure interact in a genuinely calculable way through hydraulic engineering principles, so an actual formula gives a more reliable sizing answer than a generic "one size fits most wells" rule of thumb.
What happens if I undersize my well pump?
An undersized pump can struggle to deliver adequate pressure or flow, especially with multiple fixtures running at once, leading to weak water pressure throughout the house — right-sizing up front avoids that everyday frustration.
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