Well Pump Sizing Chart

Well Pump HP and GPM by Depth and Bathroom Count

This table shows recommended HP class and approximate available GPM for common residential well depths and bathroom counts. GPM demand: 1–2 baths = 8 GPM, 3–4 baths = 12 GPM, 5+ baths = 18 GPM. TDH = well depth + 15 ft fixture lift + ~4 ft friction (1 in × 120 ft at mid-range flow) + 138.6 ft pressure head (60 PSI cut-out). HP is the smallest typical band that covers demand at that TDH. Tank size from 40/60 switch drawdown factor and 1-minute buffer.

HP is horsepower class (1/2, 3/4, 1, 1.5). ~GPM is approximate pump capacity at the computed TDH for that depth (not demand, but what the pump delivers — confirm it exceeds demand). Tank is nominal gallon size (20, 32, 44, 62, 86 common residential). \"Above 1.5\" means this depth/demand combination is past typical 1.5 HP residential territory; options include 2 HP, multi-stage, or reduce TDH (lower pressure, larger pipe, less lift).

When to Size Past the Chart

This table assumes typical residential: 1 in pipe, 120 ft run, 40/60 pressure, 15 ft fixture lift. If your install differs, the HP recommendation will shift. Common scenarios that make the chart wrong:

• Long pipe run (over 150 ft). Friction is higher. TDH goes up. You may need the next HP class. Enter actual pipe length in the calculator.
• High pressure setting (50/70 or 60/80 PSI). Pressure head is the cut-out × 2.31. A 70 PSI cut-out is 161.7 ft of head instead of 138.6. That pushes shallow wells into higher HP. Common on hillside lots or where the second floor needs strong pressure.
• Undersized pipe (3/4 in or smaller). Friction at 12+ GPM through 3/4 in pipe is much higher than 1 in. TDH increases. You may need more HP or upsize the pipe first.
• No additional fixture lift (single-story on slab). TDH is lower (no 15 ft to second floor). You may be able to drop to a smaller HP class than the table shows. Confirm with the calculator — do not just trust the lower number if you still have long horizontal runs.
• Very deep wells (over 300 ft). Multi-stage submersibles, voltage drop on the cable, and site-specific well conditions. Do not use a generic chart. Work with a well installer and confirm wire gauge, motor rating, and curve at that depth.
• Low well yield. If the driller said \"this well makes 5 GPM,\" you cannot size a pump for 12 GPM demand no matter what HP you pick. The well will run dry. Either reduce demand (low-flow fixtures, stagger use, cistern buffer) or accept the limitation. The chart assumes yield exceeds demand.

Pressure Tank Sizing Notes

The tank sizes in the table (20, 32, 44, 62 gal) are based on a 40/60 PSI switch (28% usable drawdown) and 1 minute of demand as a conservative residential buffer. Larger tanks lengthen pump cycles and reduce wear. Smaller tanks may short-cycle if someone showers while the dishwasher fills. If you already have a tank, confirm it matches or exceeds the table recommendation. If the installed tank is too small, upsize the tank before you upsize the pump — short-cycling is often a tank problem, not an HP problem.

Pre-charge: the tank's air-side pressure must be set to about 2 PSI below the cut-in. A 40/60 switch wants ~38 PSI pre-charge. If the bladder is flat or the pre-charge is wrong, the tank has no usable volume and the pump will short-cycle no matter what size tank you installed. Check pre-charge with a tire gauge at the tank's Schrader valve (power off, tank drained). Detailed tank math: sizing guide.

Submersible vs Jet Pump by Depth

Under ~25 ft: shallow-well jet pump is viable (motor at surface, pulls with suction). Budget and service access favor jet. Noise and aesthetics favor submersible if the well is near living space.

25–80 ft: convertible (deep-well) jet pump possible, but 4-inch submersibles are the residential default. Efficiency and operating cost favor submersible. Jet pumps in this range need a two-pipe ejector setup and lose efficiency with depth.

Over 80 ft: submersible only, practically speaking. Jet pumps at that depth are marginal. Confirm wire gauge and voltage drop if depth is over ~200 ft or the pump will not make rated HP. Full comparison: submersible vs jet pump.

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