Quick answer
Generator size depends on the appliances you need to run, their running watts, and their starting surge. Add the running watts for essentials, then allow headroom for the largest starting load.
Refrigerator
Often 600-800 running watts
Window AC
Often 500-1,500 running watts
Whole-home standby
Usually requires electrician sizing
Why sizing matters
A generator that is too small can overload or fail to start larger appliances. A generator that is much larger than needed costs more, uses more fuel, and can be harder to move or store.
What to check next
List the appliances you need, find both running watts and starting watts, then leave headroom for the largest surge load.
Frequently asked questions
Should I size a generator myself?
You can estimate portable generator needs, but permanent standby systems and transfer switches should be sized and installed by qualified professionals.