What Size Power Inverter Generator Do You Need?
Add up the running watts of everything you want to power at the same time, then add the extra surge of the largest motor, and pick a generator whose running and peak ratings cover that total. Most people who only need a fridge, lights, and electronics during an outage land between about 3,000 and 5,000 running watts. Running a whole house, especially with central air or electric heat, calls for the top of the inverter range, around 9,000 running watts, plus a transfer switch.
Westinghouse iGen12000TFcBest for whole-home backup
WEN DF680iXBest 240V mid-size
WEN DF480iXBest mid-size for RVsStart with running watts and starting watts
Every appliance has two numbers that matter. Running watts is what it draws once it is going. Starting (or surge) watts is the short burst a motor needs to get going, and it can be much higher than the running figure.
Generators list both. On our spec sheets you will see running watts and peak watts, such as 5,100 running and 6,800 peak on the WEN DF680iX. Size by running watts for your everyday load, then make sure the peak rating can handle the biggest motor starting while everything else is on.
How to add up your load in four steps
You do not need special tools. You need the label on each appliance and a pen.
- List only the items you truly need at the same time. Skip anything you can run later.
- Find the running watts on each label. If it only lists amps, multiply amps by volts (120 for most outlets).
- Add the running watts together.
- Find the single appliance with the biggest starting surge, usually a fridge, well pump, sump pump or air conditioner. Add its extra starting watts on top of your total.
- Add a cushion of 10 to 20 percent so the generator is not running at its limit all day.
A worked example (numbers are illustrative)
Say you want a refrigerator, a few lights, a router with chargers, and a furnace fan. Using round example figures, the fridge might run at 700 watts, lights at 100, the router and chargers at 150, and the furnace fan at 600. That is 1,550 running watts.
If the fridge needs about 2,100 watts to start, that is 1,400 more than its running draw. Your peak need is roughly 2,950 watts. Your own appliances will differ, so check the labels rather than using these figures.
For comparison, the WEN DF360iX is rated at 2,900 running and 3,600 peak watts on gasoline, so it would sit close to the line in this example. A 3,900 running watt model such as the Westinghouse iGen4500DF would leave more room.
Match the size to your use
Once you know your number, this table shows where common inverter generators from our comparison fall. Figures are gasoline ratings from the published specs.
Propane and natural gas ratings are lower. The WEN DF680iX drops to 4,500 running watts on propane, and the Westinghouse iGen12000TFc is rated at 8,100 on propane and 7,200 on natural gas. If you plan to use those fuels, size from the lower number.
| Use | Running watts to look for | Example from our data |
|---|---|---|
| Phones, laptops, a small camp setup | Under 3,000 | WEN DF360iX, 2,900 running, 49 lb |
| Camping or tailgating with more gear | 3,000 to 3,500 | PowerSmart DB5035, 3,200 running; Oxseryn 4400W, 3,400 running |
| Mid-size RV or essentials during an outage | 3,900 to 4,000 | Westinghouse iGen4500DF, 3,900 running; WEN DF480iX, 4,000 running |
| Larger backup with 240V | About 5,000 | WEN DF680iX, 5,100 running, 240V outlet |
| Whole-home backup | 9,000 | Westinghouse iGen12000TFc, 9,000 running, 191 lb |
What size inverter generator can run a house?
It depends on what your house runs on. A home with gas heat and gas cooking, where you only want to power the fridge, lights, outlets and a few other circuits, can often get by with a mid-size unit in the 4,000 to 5,100 running watt range.
Whole-house power is a different story. Central air conditioning, an electric range, an electric water heater and an electric dryer all draw a lot. Inverter generators in our comparison top out at 9,000 running watts, so even the largest one will not run everything at once. Most people choose a large model and pick the circuits that matter most.
For that setup, look for a 240V outlet and transfer switch or interlock kit readiness. The Westinghouse iGen12000TFc lists both a 50A and a 30A outlet that are ready for a transfer switch or interlock kit. Have a licensed electrician install the switch. Never plug a generator into a wall outlet, because it can send power back into the grid and injure utility workers.
Other things that affect the right size
Wattage is only part of the decision. Fuel type changes your usable power, as noted above. Weight matters if you will move the unit often. In our data, weights run from 39 lb to 191 lb, so a big model is not something you will carry to a campsite.
Noise also varies. Our listed inverter generators run from 51 to 72 dBA, and the Westinghouse iGen4500DF is listed as low as 52 dBA. For a quiet campsite, a smaller, quieter unit may beat a larger one. You can see all of this side by side on our best power inverter generator page.
If you are not sure an inverter model is the right type at all, our best generator page covers other kinds, such as conventional portable units. And if you only need small loads from a vehicle battery, a plain power inverter, not a generator, is a different tool. See our best power inverter page for those.
Safety notes before you buy and run one
Never run a generator indoors, in a garage, or near windows, doors or vents. Carbon monoxide can build up quickly and you cannot smell it. Place the unit outside, well away from the house, with the exhaust pointed away from openings.
A built-in CO shutdown sensor adds a layer of protection, and several models in our comparison include one. It does not replace safe placement or a working CO alarm inside your home.
Let the engine cool before refueling, store fuel in approved containers, and keep the generator dry. Wear hearing protection if you will work close to a running unit, and use properly rated outdoor extension cords.
Frequently asked questions
Is it better to buy a bigger generator than I need?
A little extra capacity is useful, but a much larger unit costs more to buy, weighs more and burns more fuel for small loads. Aim for your calculated total plus a modest cushion.
Can a small inverter generator run a refrigerator?
Often yes, as long as its running and peak ratings cover the fridge's starting surge plus anything else on at the same time. Check the fridge label for its running watts.
Do I need a 240V outlet?
Only if you have 240V equipment, such as a well pump or a home transfer switch for larger circuits. Among our examples, the WEN DF680iX and Westinghouse iGen12000TFc list 240V outlets.
Can I link two smaller generators instead of buying one large one?
Some models are parallel ready, which lets you pair two compatible units. The Westinghouse iGen12000TFc lists parallel readiness. Check that your model supports it and use the correct cable.