Step 1: Decide which appliances you want to power at the same time
Step 2: Determine the maximum total load for these appliances, including start up requirement.
This is usually given in watts and can be found on the data plate or in the manual for the appliance. Starting power is higher than running power for appliances with electric motors and compressors, such as air conditioners, so it is important that you get this information. Often it is not found in manuals and you may need to contact the manufacturer.
Step 3: Choose a generator that can handle the maximum load.
Hint #1: Generators are sized in kVA, if the rated output in watts is not given multiply the kVA by 0.8. This will give you the rated output for the generator in kW (multiply again by 1000 to get the number of watts).
Hint #2: Because many appliances require additional power for starting than running, you may be able to use a smaller generator if you don’t start all of the appliances at once, or if you turn some off while using others.