Generator size by appliance / well pump
What size generator runs a well pump
Well pump, 1/2 hp: 1,000 W running plus 2,100 W more for a few seconds as it starts, so a generator needs at least 3,100 W of starting capacity to run it on its own. The smallest of the six portables this site covers that can do it is the Westinghouse iGen5000 (3,900 W running, 5,000 W peak).
Without power a private well delivers no water, so the well pump is often the reason a rural household buys a generator. Check the motor label for its voltage: many well pumps run on 240 volts, and the two smallest Honda inverters here supply 120 volts only.
The pump motor's maker publishes its own minimum generator sizes. Franklin Electric's manual sets a higher floor for 2-wire submersible motors than for 3-wire ones: 3 kW against 2 kW at 1/2 hp, and 6 kW against 4 kW at 1 hp. For a submersible pump, the motor maker's table is the one to follow.
For sizing the pump itself, see Well Sizer, which works from the Goulds selection chart.
The figures and where they come from
| Device | Source | Running W | Additional starting W | Starting need alone |
|---|---|---|---|---|
| Well pump, 1/2 hp | Generac GP brochure (2023) | 1,000 | 2,100 | 3,100 |
| Well pump, 1/3 hp | EWEB (2019) | 1,000 | 2,000 | 3,000 |
Highlighted rows are the figures the calculator uses. Every table here prints additional starting watts: the surge on top of running watts.
Franklin Electric's minimum generator sizes
| Motor | 2-wire motor | 3-wire motor |
|---|---|---|
| 1/3 hp | 2.25 kW | 1.5 kW |
| 1/2 hp | 3 kW | 2 kW |
| 3/4 hp | 4.5 kW | 3 kW |
| 1 hp | 6 kW | 4 kW |
| 1.5 hp | 7.5 kW | 5 kW |
Franklin Electric AIM Manual, 60 Hz submersible systems (2026), Generator Minimum Rating table: "Generators must be sized to deliver at least 65% of the motor's rated nameplate voltage during starting."
Which portables can run it
| Generator | Running / peak W | Alone | With fridge, 6 LED bulbs, 2 chargers |
|---|---|---|---|
| Honda EU2200i | 1,800 / 2,200 | No | No |
| Honda EU3000iS | 2,800 / 3,000 | No | No |
| Westinghouse iGen5000 | 3,900 / 5,000 | Yes | Yes |
| Honda EU7000iS | 5,500 / 7,000 | Yes | Yes |
| Champion 201040 | 7,500 / 9,375 | Yes | Yes |
| Westinghouse WGen9500DF | 9,500 / 12,500 | Yes | Yes |
A generator fits when its running rating covers every running watt and its peak (or "max") rating covers the running total plus the single biggest starting surge. Adding the basics — a refrigerator (700 W running, 2,200 W to start), six 15 W LED bulbs and two phone chargers — raises the running load to 1,830 W and the starting need to 4,030 W, because the refrigerator's surge is now the biggest one. The smallest portable here that covers that is the Westinghouse iGen5000.
On a standby generator
A home standby unit is rated in kilowatts and has no overload capacity: Generac's rating definition says "No overload capability is available for this rating." Using Generac's own formula — sum of running watts plus the highest single starting burst — the well pump with the basics needs 4 kW. The smallest Guardian model that covers it on natural gas is the 10 kW, rated 9 kW on natural gas and 10 kW on propane, which leaves 5 kW of starting room for everything else. Whole-home lists are on the standby generator pages.
Well pump, 1/3 hp
The smaller size needs 1,000 W running and 2,000 W more to start, 3,000 W in all; the Honda EU3000iS is the smallest portable here that starts it alone. With the basics it needs 4,030 W to start.
Before running anything, read the carbon monoxide distance rules and how a transfer switch keeps power off the utility lines. Other appliances: refrigerator · sump pump · furnace · window AC · central air · heat pump · space heater · water heater · washing machine · garage door opener · CPAP · oxygen concentrator.