Well Pump Sizing Calculator
Enter your required flow rate and total dynamic head — get the recommended pump horsepower.
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Jet pump vs submersible pump
This calculator's formula applies to either type — the difference is mechanical, not mathematical. A jet pump sits above ground and pulls water up through suction, which limits it to shallow wells (roughly 25 ft or less in practice, since suction lift has a hard physical ceiling). A submersible pump sits down in the well itself and pushes water up, which works for wells of any practical residential depth and is the more common choice for anything beyond a shallow well. If your calculated head is high — deep well, long horizontal run, or significant elevation to the pressure tank — a submersible is almost always the right category to be shopping in, independent of the exact horsepower this calculator returns.
How to use this calculator
Enter the flow rate you need the pump to deliver, the total dynamic head it has to work against, and the
pump's efficiency (use the manufacturer's curve if you have it, or 50% as a typical estimate for small
submersible pumps). This runs the standard hydraulic horsepower formula:
BHP = (GPM × TDH) / (3960 × efficiency).
What "total dynamic head" actually includes
TDH isn't just the well's depth — it's the vertical lift from the water's pumping level up to the pressure tank, plus friction loss through the pipe, plus the pressure you want maintained at the tank. A rough field estimate many well contractors use is roughly 1.5× the well depth to account for these added factors, but a precise calculation (or your well driller's report) gives a more accurate number. See total dynamic head explained for the full breakdown.
Worked example
10 GPM required, 150 ft TDH, 50% pump efficiency: BHP = (10 × 150) / (3960 × 0.5) = 0.76 HP, which rounds up to a standard 1 HP pump.
Frequently asked questions
What flow rate should I design for?
Size for your home's peak simultaneous demand, not average usage — a common starting point is 8-12 GPM for a typical single-family home, higher if you're also covering irrigation or livestock.
Why does pump efficiency matter so much to the result?
Efficiency is in the denominator of the formula, so a less efficient pump needs proportionally more horsepower to deliver the same GPM at the same head — a pump rated 40% efficient needs noticeably more HP than one rated 55% for an identical job.
Is it better to oversize a well pump "to be safe"?
Not really — an oversized pump cycles on and off more frequently, which increases wear, and draws more power than necessary. Sizing to the actual calculated requirement (rounded to the nearest standard size) is the right target, not deliberately going a size or two over.
Based on the standard hydraulic horsepower formula. Reference only — actual system design should also account for your specific pump curve and well characteristics. Consult a licensed well contractor before installing.