Generator Power Output Ratings
The most contentious topic regarding generators is the output rating. They are advertised output ratings are quoted in Watts.
A basic rule of thumb is that the generator is outputting 120 VAC so the wattage rating is equal to (the calculation is simple Ohm's law Amps = Watts / Voltage) so if a device that is rated at 1 amp at 120 VAC = 120 watts. Two things complicate the calculation. The first is that if the device has a motor it will draw a significantly higher amount of power than while it is running (this is known as spin up). The second issue is that the manufacturers fudge the numbers. Much like the output rating system for car stereo systems the advertised output rating is rarely ever the same on any two different brands. I have seen as much as 1000 watt differences in load tests. So do your homework and make sure that you give yourself some head room on the wattage rating.
There are several issues when selecting the size of a generator that you need to consider. Your basic power demands are the first consideration. I have provided an example below: (try the calculator at Honda) http://powerequipment.honda.com/generators/wattage-calculator