There are different categories to consider when choosing a generator for your needs: recreation, home standby and construction. You may also want to consider using an inverter generator for sensitive electronic devices. Inverter generators are smaller and lighter as power is created electronically and not through a conventional alternator. Inverter power offers the cleanest power output.
 

If you want a generator for home standby, say to run your refrigerator, you’ll need at least 2500 watts or more. And if you want to use a transfer switch so that power can go directly into your home, you’ll want a generator with at least 3000 watts.
 

You’ll also need to consider the maximum and rated power of the generator. This is important depending on what items you want to run off of your generator. Items such as toaster, lamps, and coffee makers are resistive, or constant loads and their total load can be calculated at amps x 1. Items such as saws and drills are reactive loads and while the running load may be small, the starting load should be calculated at running amps x 3. Remember, after the intial start less power is required for actual operation.
 

Always remember that simple power management will allow a smaller generator to do a big job. Very seldom are all tools or appliances operating simultaneously. When calculating power requirements, consider the starting requirements are only for the initial start and then additional tools may be operated in addition.
 

Remember Ohm’s Law
Watts = Volts x Amps
Amps = Watts/Volts

So, if you have two of the numbers (e.g. volts, amps) then you can find out the other (e.g. watts). This can help you to determine the rated power that you’ll need from your generator.