What size generator to run a well pump?
Using the top of Champion’s range for a 1 hp well pump (2,000 running, 4,000 starting watts), plan on a generator with at least 2,500 W running and 4,000 W starting watts — and check whether your pump runs on 240 V.
How to work it out
- Running total 2,000 W × (1 + 25% headroom) = 2,500 W running
- Running total 2,000 W + biggest start-up extra 2,000 W = 4,000 W → 4,000 W starting
Well pumps are among the hardest loads for a portable generator: a big motor, often deep in the well, that needs a large surge to start and often runs on 240 V. Champion’s chart gives 1,000–2,000 running and 2,000–4,000 starting watts for 1 hp, and 750–1,000 / 1,500–2,000 for ½ hp.
Adjust for your project
More options: Headroom
- Running watts
- 2,500 W
- Starting (peak) watts
- 4,000 W
- Running watts, all together
- 2,000 W
- Biggest single starting surge (extra)
- 2,000 W
- Running current at 120 V
- 16.7 A
- Start the biggest motor first, then add the other loads one at a time — the generator only has to cover one start at once.
Generator size with other headroom
| Headroom on running watts | Running watts | Starting (peak) watts |
|---|---|---|
| 0% | 2,000 W | 4,000 W |
| 10% | 2,200 W | 4,000 W |
| 25% | 2,500 W | 4,000 W |
| 50% | 3,000 W | 4,000 W |
What to know about generators and well pumps
- 120 V or 240 V? Many submersible pumps run on 240 V, which needs a generator with 120/240 V output and a connection through a transfer switch — not a household outlet. Check the pump control box or breaker.
- Read the motor label. A pump’s service amps or locked-rotor amps give a better figure than any chart; the pump installer or the control box label usually lists them.
- Run it on its own. Let the pump start with little else running, then add other loads. Its pressure switch will cycle it on and off as you use water.
- Bigger pumps, bigger generators. Above 1 hp, go by the pump’s own label or ask the installer — the chart stops at 1 hp.
For a whole-house outage plan that includes the pump, see what size generator to run a house. On solar, another big motor load is worked through on how many solar panels to run a pool pump.
Different size? Use the full Generator Size Calculator.
What you’ll need
- Dual-fuel portable generatorPremium price
Runs on gasoline or propane. Propane stores for years without going stale; expect somewhat fewer watts on propane.
See options on Amazon (opens in a new tab) - Battery-operated carbon monoxide alarmBudget price
CPSC advises battery or battery-backup CO alarms whenever a generator is in use. Look for UL 2034 certification and test monthly.
See options on Amazon (opens in a new tab) - Outdoor generator extension cordMid-range price
Lets the generator sit well away from the house. CPSC says to use outdoor-rated cords whose rating exceeds the total load, with all three prongs.
See options on Amazon (opens in a new tab)
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Frequently asked questions
What size generator to run a ½ hp well pump?
About 1,250 W running and 2,000 W starting watts (top of Champion’s ½ hp range).
What size generator to run a well pump and a refrigerator?
About 2,750 W running and 4,200 W starting, starting the pump first.
Other common sizes
- What size generator to run a refrigerator — 1,200 W starting — a 2,000 W-class generator
- What size generator to run a house — 4,550 W running / 4,740 W starting
Sources
- Champion Power Equipment — Generator Wattage Chart (opens in a new tab) — Typical running and starting watts for household, RV and job-site appliances (a manufacturer’s planning chart — your nameplate wins).
- Virginia Cooperative Extension, BSE-301: Estimating Appliance and Home Electronic Energy Use (2020) (opens in a new tab) — Wattage × hours ÷ 1,000 = kWh per day; watts = amps × volts when only amps are listed; a refrigerator runs at full wattage about a third of the time; typical nameplate wattages.
- ENERGY STAR — Certified Televisions data set (on-mode power) (opens in a new tab) — Certified models, on-mode watts, retrieved October 2026: 32 in about 27–36 W; 43 in about 45–78 W; 50 in about 61–90 W; 55 in about 64–114 W; 65 in about 85–135 W; 75 in about 120–176 W.
- U.S. Consumer Product Safety Commission — Portable Generator Hazards (Safety Alert 5123, 2021) (opens in a new tab) — Never run a generator indoors or in a garage, even with doors open; place it outside far from doors, windows and vents; CO alarms; never “backfeed” by plugging into a wall outlet.
- U.S. Consumer Product Safety Commission — CPSC Warns Consumers in Path of Storms to Take Precautions When Using Portable Generators (July 24, 2020) (opens in a new tab) — “Use your generator OUTSIDE your house ONLY, at least 20 feet from your home”; make sure you have working CO alarms.
- OSHA Fact Sheet — Using Portable Generators Safely (opens in a new tab) — Never attach a generator to a building’s wiring unless a qualified electrician has installed a transfer switch; 3–4 ft of clear space around the unit.
- Champion Power Equipment — 3500-Watt Dual Fuel Generator (model 201213) specifications (opens in a new tab) — 3,500 running / 4,000 starting watts on gasoline; 14 h at 50% load on 4.7 gal; 10.5 h at 50% load on a 20 lb propane tank; 120 V 30 A TT-30R RV outlet.
- Champion Power Equipment — 6500-Watt Dual Fuel Generator (model 201077) specifications (opens in a new tab) — 6,500 running / 8,125 starting watts on gasoline (5,850 / 7,325 on propane); 11 h at 50% load on 7.7 gal; 6.5 h at 50% load on a 20 lb propane tank.
- Champion Power Equipment — 2000-Watt Dual Fuel Inverter (model 201230) specifications (opens in a new tab) — 1,700 running / 2,000 starting watts on gasoline (1,530 / 2,000 on propane); 11.5 h at 25% load on 1.05 gal; 34 h at 25% load on a 20 lb propane tank.