How to Size a Portable Generator for Your House

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Step 1: List what you actually need to run

Start with the loads that matter during an outage, not the whole house. Most people pick a short list: the refrigerator, some lights, phone and laptop charging, the internet equipment, and maybe a furnace blower, sump pump, or window unit.

Then decide which of those need to run at the same time. You can often take turns with the rest, like running the microwave only when the fridge is not starting up. The fewer things on at once, the smaller the generator you need.

Step 2: Find your own wattage numbers

Do not guess, and do not rely on typical figures from a chart. Draws vary a lot from model to model. Find the real number for each item you own.

Motors, like those in refrigerators, freezers, pumps, and air conditioners, pull a short burst of extra power when they start. That burst is the starting watts. If a label does not list it, the owner's manual or the maker's support line can tell you, or an electrician can help estimate it.

• Check the data plate or label on the appliance, often inside the door or on the back.
• Read the power brick or charger for electronics.
• Look up the model on the maker's spec page or in the owner's manual.
• Use a plug-in watt meter for anything that plugs into a wall outlet.
• For hardwired loads like a furnace or well pump, ask an electrician to read the label or measure it.

Step 3: Do the math and leave headroom

Add the running watts of everything you want on at once. That total is the minimum running-watt rating you need. Then take the one item with the biggest starting surge and add its extra starting watts to that total. That is the minimum starting-watt rating you need. Champion's manual says to start the generator with nothing plugged in, connect the largest motor first, let the engine settle, and then add the other loads one at a time. That is why you size for one surge.

For example, if your running loads add up to 2,000 watts and your biggest motor needs an extra 1,500 watts to start, look for a generator rated for at least 3,500 starting watts and comfortably more than 2,000 running watts.

Do not size right to the edge. A generator running near its limit for hours works harder, burns more fuel, and has no room for a load you forgot. Pick a unit with clear margin over both totals.

Step 4: Read the spec sheet, not just the name

Generator names usually feature one big wattage number. On many units that is the starting or peak figure, and the running rating is lower. Find both numbers on the spec sheet and compare each to your totals.

Dual fuel units often list separate ratings for gasoline and propane, and the propane figures are often lower. If you plan to run on propane, size to the propane numbers.

Inverter generators produce steadier power, which is a good match for computers, TVs, and chargers. Also check the outlet layout. Some loads, like many well pumps and central air systems, need 240 volts, and many portable units offer only 120-volt outlets. Finally, look at the maker's runtime chart at a load close to yours, not just at a light load.

Step 5: Connect it safely

Run the generator outdoors, well away from the house, with the exhaust pointed away from doors, windows, and vents. Never run it indoors, in a garage, or in a carport. Put a battery-powered carbon monoxide alarm inside the home.

You can run individual appliances on outdoor-rated extension cords sized for the load. To power circuits in your house, you need a transfer switch or interlock installed by a licensed electrician. Never plug a generator into a wall outlet. Inlets and outlets come in different plug types, so ask your electrician which outlet on your generator is right for your setup and whether any adapter is safe to use.

If you want the whole house covered automatically, a home standby generator is a different class of product and is worth a separate look.

Sources

Recorded AI check: Oct 30, 2026. The sources below may include later additions. AI checks compare factual numbers and checkable claims with web sources; they do not verify every statement.

• Generator Wattage Chart - Champion Power Equipment
• What Size Generator Do I Need? - Champion Power Equipment
• 4000W Dual Fuel Inverter - 201050 - Champion Power Equipment
• Champion 201302 Operator's Manual (PDF)
• Franklin Electric AIM Manual, 60 Hz Submersible Systems, 2026 Edition (PDF)
• Choosing the Right Size Generator for Your Home AC | Micro-Air

Best inverter generator for a home outage compares units from the makers' numbers. Every guide in this class is in Portable generators.

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