Generator sizing calculator
Tick the things you want to run during an outage. You get the running watts and starting watts a generator needs to cover them.
Tick at least one item or enter some watts
Wattages come from published appliance charts from Eugene Water and Electric Board (EWEB). Method: add the running watts of everything you will run, then add only the largest extra starting load. Check the label on your own equipment, since real values vary by model.
How this calculator works
Every appliance has a running wattage. Motors, like a refrigerator compressor or a sump pump, also need a short burst of extra power to start. To size a portable generator, add up the running watts of everything that will run, then add only the largest single starting surge, because motors rarely start at the exact same instant.
The result is rounded up to the nearest 50 watts, and the running figure includes a 10 percent cushion so the generator is not pushed past about 90 percent of its capacity.
Frequently asked questions
What size generator do I need to run a refrigerator?
A typical refrigerator uses about 700 running watts and needs about 2,200 more to start. A generator rated for roughly 2,900 starting watts covers it by itself.
What is the difference between running watts and starting watts?
Running watts are what an appliance draws continuously. Starting watts, or surge, are the brief extra draw when a motor kicks on. A generator needs to cover the running total plus the largest surge.
Can I power my whole house with a portable generator?
Not with a small one. Central air conditioning, electric ranges, and electric water heaters use thousands of watts each. Whole-house backup needs a properly sized unit connected through a transfer switch by an electrician.
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Last updated October 2026. Reviewed by the Fix or Hire editorial team. Estimates only, not a quote.