What size generator do I need in 2026?
Size a home generator by what you need to run, not by square footage. Back up the essentials and most homes need 5,000 to 7,500 running watts; run the whole house with central AC and you are into 18 to 24 kW standby territory. Here is how to get your own number, and the safety rules that matter.
Sizing a generator in five steps
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List what you must run at once
Write down the appliances you cannot go without in an outage: the fridge, a freezer, the furnace blower, a sump or well pump, some lights. Be honest about needs versus wants.
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Add up the running watts
Sum the running watts of everything on the list. This is the steady load the generator carries the whole time it runs.
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Add the single largest starting surge
Find the one appliance with the biggest startup surge (usually a pump or compressor) and add only that surge on top of the running total. Do not add every surge; motors do not all start at once.
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Add headroom and round up
Add roughly 20 to 25 percent so the generator is not running flat out, then round up to a standard size.
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Pick portable or standby
If the number fits a common portable, a portable plus a transfer switch runs your essentials. If it is large, or you want the whole house and central AC, that is a standby install.
The two numbers that matter
Every generator sizing question comes down to running watts and starting watts. Running watts are the steady draw once an appliance is going. Starting watts are the brief surge a motor pulls the instant it starts: a fridge that runs at 700 watts can spike to 2,200 for a fraction of a second. You size to the running total plus the single largest surge.
Here is what a typical essentials set looks like. The full set is on the appliance wattage chart.
| Appliance | Running (W) | Starting (W) |
|---|---|---|
| Refrigerator or fridge-freezer | 700 | 2,200 |
| Chest or upright freezer | 500 | 1,500 |
| Sump pump (1/3 HP) | 750 | 1,500 |
| Well pump (1/2 HP) | 1,000 | 2,100 |
| Gas furnace blower (1/2 HP) | 800 | 2,350 |
Gas, propane, or dual fuel
Gasoline portables are the cheapest and most common, but gas goes stale and is hard to get right when the power is out. Propane stores for years and runs cleaner, which is why many people pick a dual-fuel portable or a propane standby. If you are on propane, see how long a tank lasts at your load.
The rules that keep people alive
- Never plug a generator into a wall outlet to power your house. This backfeeding can electrocute a lineman and start a fire. A licensed electrician installs a transfer switch, the only safe way to feed house circuits.
- Never run a generator indoors, in a garage, or near a window. The exhaust is carbon monoxide, invisible and deadly. Keep it outside and well away from the house.
- Sizing here is a planning estimate, not an electrical load calculation. A licensed electrician sizes the real install.
Common questions
What size generator do I need for my house?
For the essentials (a fridge, a freezer, the furnace blower, a sump or well pump, and lights) most homes land between 5,000 and 7,500 running watts, which a mid-size portable covers. Running the whole house including central AC is standby territory, usually 18 to 24 kW. The exact number comes from the appliances you choose, not the square footage.
What can a 7,500 watt generator run?
A 7,500 running-watt portable comfortably runs a full set of essentials at once: a refrigerator, a chest freezer, a well or sump pump, the furnace blower, several lights, and a few outlets for phones and a router, with headroom for the pump's startup surge. It will not run central air conditioning, which needs its own large surge budget.
Is a standby or a portable generator better?
A portable is cheaper and runs your essentials through a transfer switch, but you set it up and refuel it yourself. A standby is permanently installed, starts itself when the power drops, and can run the whole house, at several times the cost. Portables suit occasional outages; standby suits homes that lose power often or cannot go without.