To determine which generator is right for your needs, you must first add up the wattage of tools, appliances and motors you want to run at the same time. Then select a generator with the RUNNING wattage rating to match or exceed the total load. Keep in mind that tools and appliances with electric motors require additional tool/appliance SURGE wattage at startup that can be double or triple the normal running wattage requirement. Look at the surge watts required and make sure you choose a generator with enough additional wattage to start them. Keep in mind that you typically are not starting more than half of the items at the same time.

Generators are rated by output in wattage which takes into account the amperage at both 120 and 240 volts. NOTE: Volts x Amps = Watts (i.e.: 120 volts x 10 amps = 1200 watts) OR Watts/Volts = Amps. For example, a 5000 watt rated generator is capable of producing 20.8 Amps @ 240 Volts or 41.6 amps @ 120 volts. See the following chart for power ratings for common household appliances.
ITEM RUNNING WATTS SURGE WATTS
Furnace Fan (gas or oil only) 1/8 HP 300 500
1/6 HP 500 750
1/4 HP 600 1000
1/3 HP 700 1400
1/2 HP 875 2100
Refrigerator 700 2200
Microwave Oven 625 800
Coffee Maker 1750
0
Toaster 1050-1600 0
Electric Range/Oven 12,500 0
Well Pump 1/3 HP 750 1400
  1/2 HP 1000 2350
Sump Pump 1/3 HP 800 1300
  1/2 HP 1050 2150
Lights On Bulb

Television 300 0
Garage Door Opener 1/4 HP 550 1100
  1/3 HP 750 1400
Portable Heater 100-1500 0
Hair Dryer 1100-1600 0
Iron 1200 0
Water Heaters Gas 500 1500
  Electric 7000-7500 0
Computers Desktop 600-800 0
  Notebook 200-250 0
  Monitor 200-250 0
Printer 400-600 0
Fax Machine 600-800 0
Cordless Telephone 100 0
These are only estimated wattages, Please check your particular appliance for actual wattage.