Well Pump Electrical & Sizing Calculator - HP, Wire Size & Control Box for Residential Wells
Size the pump motor, wire run, control box, and breaker for deep and shallow wells
Free well pump planning calculator for homeowners, electricians, and well drillers. Enter well depth, static water level, drawdown, desired flow rate, and a friction-loss allowance to screen total dynamic head, then pick a motor HP for planning. Enter the wire run distance to get a planning wire gauge patterned after NEC ampacity and a 3 percent voltage-drop target, a planning breaker size, and a voltage drop check. Final pump selection comes from the manufacturer curve at the computed TDH, and submersible drop cable must follow the pump manufacturer cable chart. Well pump circuits are unique in residential wiring - they run on dedicated 240V circuits with long wire distances, specialized control boxes, and motor characteristics that don't follow standard branch circuit rules. A 1-HP submersible at 300 feet of depth on 400 feet of wire demands careful review: undersized wire can cause low voltage at the motor, more current draw, more voltage drop, overheating, and premature failure. This calculator flags that risk by checking voltage drop over the actual run length at the planning current draw - then the manufacturer cable chart and a licensed electrician confirm the final wire.
Check voltage drop on the pump feeder - 400 feet of well wire needs careful gauge selection
Voltage Drop Calculator →Check panel-capacity questions for the dedicated 240V pump circuit before breaker and conductor review
Panel Load Study →Set up safe generator backup so your well runs during power outages
Generator Backfeed Checker →Running irrigation off the same well? Screen pump and pipe prompts for agricultural flow rates
Irrigation Pump & Pipe Calculator →How It Works
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Enter Well Data
Input total well depth, static water level (depth to water when pump is off), and drawdown (how much the level drops during pumping). Your well driller's report has these numbers. If you don't have a report, a static level test with a weighted tape gives you the baseline.
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Specify Flow and Friction Allowance
Enter desired flow rate in GPM and a friction-loss allowance in PSI for the drop pipe and plumbing. Residential wells typically produce 5-15 GPM. The app does not compute pipe friction from diameter - use a pipe friction table or the manufacturer data for the allowance.
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Calculate Total Dynamic Head
The calculator adds pumping water level, your friction-loss allowance, system pressure, and discharge elevation to get TDH in feet. Use the TDH with the pump manufacturer performance curve to select the motor HP you screen here.
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Enter Wire Run Distance
Measure from your panel to the wellhead horizontally, then add the pump setting depth. This total one-way distance is critical for wire sizing. The calculator screens wire size using NEC-patterned ampacity and a 3 percent voltage-drop target at running amps; the pump manufacturer cable chart and actual motor/control data control the final cable.
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Review Planning Outputs
Get TDH, planning wire gauge, planning breaker size, pressure-tank cycle screening, and a voltage-drop check. The wire pick is the larger of the ampacity and 3 percent voltage-drop selections.
Built For
- Homeowners replacing a failed well pump and verifying the existing wire is adequate
- Well drillers screening pump and wire prompts for new residential installations
- Electricians running a new circuit to a well after the existing wire is damaged
- Rural property owners adding a well for a second dwelling or shop
- Property buyers evaluating the adequacy of an existing well system before purchase
Assumptions
- Well yield (GPM) is sufficient to meet the calculated demand without drawdown below pump intake.
- Total dynamic head (TDH) includes static water level, drawdown, friction loss, and pressure tank set point.
- Wire sizing is an estimate patterned after NEC ampacity (125% FLA, 75C copper) and a 3% voltage-drop target; the pump manufacturer cable chart controls the final cable.
- Pressure tank is pre-charged to 2 PSI below the cut-in pressure of the pressure switch.
Limitations
- Does not model variable-speed (constant pressure) pump systems or VFD-driven well pumps.
- Cannot account for well recovery rate or intermittent yield from low-producing wells.
- Does not select the pressure tank beyond screening drawdown volume and cycle rate.
- Friction loss is user-entered and not calculated from exact drop-pipe geometry.
References
- NEC Article 430 - Motors, Motor Circuits, and Controllers (wire sizing and overcurrent protection)
- Franklin Electric AIM Manual - Submersible Motor Application, Installation, and Maintenance
- Water Systems Council - Well Owner's Handbook (residential well system sizing guidelines)
- Hydraulic Institute Standards - Pump System Assessment and Optimization