What Size Generator Do I Need to Run a Well Pump?
Submersible well pump motors require 3 to 5 times their running wattage just to break static inertia and start against a column of water. Sizing a generator solely on running watts will cause the generator's voltage to collapse upon pump startup.
- 0.5 HP (1/2 HP): 1,000 Running Watts | 3,500 – 4,000 Starting Watts
- 0.75 HP (3/4 HP): 1,500 Running Watts | 4,500 – 5,000 Starting Watts
- 1.0 HP (1 HP): 2,000 Running Watts | 5,500 – 6,500 Starting Watts
- 1.5 HP (1-1/2 HP): 2,600 Running Watts | 7,500 – 8,500 Starting Watts
- 2.0 HP (2 HP): 3,300 Running Watts | 9,500 – 11,000 Starting Watts
- 3.0 HP (3 HP): 4,500 Running Watts | 14,000 – 16,000 Starting Watts
- 5.0 HP (5 HP): 7,500 Running Watts | 22,000 – 25,000 Starting Watts
⚡ Interactive Generator Size Calculator for Well Pumps
What Size Generator to Run a Well Pump and Refrigerator?
To run both a standard 1.0 HP (230V) submersible well pump and a household refrigerator simultaneously during an outage, you need a generator with at least 7,500 Starting (Surge) Watts and 3,500 Continuous Running Watts.
The Dual-Startup Math: A 1 HP well pump requires 6,000W starting surge and 2,000W running. A modern refrigerator compressor requires ~1,200W starting surge and 300W running. If both compressors start at the same time, peak surge demands 7,200W to 7,500W. Sizing to an 8,000W or 8,500W dual-fuel generator with a 30A 240V (L14-30R) outlet prevents voltage sag and breaker trips.
Why Well Pumps Stall Small Generators (Locked Rotor Amps)
When a pressure switch closes, the submerged motor draws its Locked Rotor Amps (LRA) for the first 0.3 to 0.5 seconds. For a 1 HP 230V motor drawing ~8 FLA continuously, starting LRA surges to 35 to 44 Amps.
If your generator cannot supply this instant surge, its engine will bog down, tripping the breaker and starving the start capacitor.
| Pump Motor Size | Supply Voltage | Running Watts | Required Starting Watts | Recommended Generator Size |
|---|---|---|---|---|
| 0.5 HP (1/2 HP) | 115V or 230V | 900W – 1,100W | 3,500W | 4,500W Inverter / Portable |
| 0.75 HP (3/4 HP) | 230V | 1,300W – 1,600W | 4,800W | 6,000W Dual-Fuel Generator |
| 1.0 HP (1 HP) | 230V | 1,800W – 2,200W | 6,000W | 7,500W – 8,500W Portable Generator |
| 1.5 HP (1-1/2 HP) | 230V | 2,400W – 2,800W | 8,000W | 9,500W – 12,000W Standby / Dual-Fuel |
| 2.0 HP (2 HP) | 230V | 3,000W – 3,500W | 10,500W | 12,000W+ Whole-House Generator |
| 3.0 HP (3 HP) | 230V | 4,200W – 4,800W | 14,000W | 15,000W – 18,000W Standby Generator |
| 5.0 HP (5 HP) | 230V | 7,000W – 8,000W | 22,000W | 22,000W+ Commercial Standby Generator |
Verify Your System Parameters:
Calculate your Total Dynamic Head with our TDH Calculator, size your pressure tank with the Pressure Tank Calculator, or verify wire gauge in the Wire Size Calculator.