The answer to 'what size generator do I need' is that the size of the generator you need depends on the total wattage of the appliances and devices you want to power during an outage. As a general rule, you'll want a generator that can provide at least 5,000 to 7,500 watts of power to handle essential items like refrigerators, lights, and some small appliances. For a whole-home backup, you may need a generator in the 10,000 to 20,000 watt range.
To determine the right size generator, make a list of all the items you want to power and add up their total wattage. This will give you a good starting point. Keep in mind that starting wattage for motors and compressors can be 2-3 times higher than their running wattage, so you'll want to account for that as well. It's also a good idea to have some extra capacity, around 20-30% more than your total wattage needs, to handle future changes or additions to your home.