How generator sizing works
Generator sizing comes down to one simple formula used by electricians and manufacturers alike:
Starting watts needed = total running watts + the largest single starting surge
Why only the largest surge? Motors start for a fraction of a second, and it's unlikely that two will kick on in the exact same instant. You can make sure of it by switching appliances on one at a time after the generator starts. That's called staggering.
Portable vs. inverter vs. standby
| Type | Typical size | Best for |
|---|---|---|
| Inverter generator | 2,000–4,500 W | Quiet, clean power for electronics, fridges, RVs |
| Portable (open-frame) | 5,000–12,000 W | Whole-home essentials through a transfer switch |
| Home standby | 10,000–26,000 W | Automatic whole-house backup on natural gas or propane |
| Battery power station | 1,000–6,000 W | Indoor-safe, silent backup with no fuel or fumes |
Safety first
- Never run a fuel generator indoors, in a garage or near windows. Generator exhaust kills dozens of people in the U.S. every year. Keep it at least 20 feet from the house with the exhaust pointing away.
- Never backfeed the house through a dryer outlet. Use a properly installed transfer switch or interlock kit; backfeeding can electrocute utility workers.
- Put battery-powered CO alarms on every floor.
If fumes, noise or fuel storage are a concern, a battery power station can be used indoors. Use the power station size calculator to compare.