What Size Generator Do I Need?
Check your appliances, set a safety margin, and read the recommended generator size.
Pick the appliances you want to run
Check every device you expect to run at the same time. Add a quantity for multiples like several lights or power tools. Press Calculate to see your running watts, the worst-case startup surge, and the generator size we recommend with headroom.
How the number is built
A generator is sized by its surge (starting) watts, not just its running watts. Motors inside fridges, well pumps, sump pumps, furnaces and air conditioners draw two to three times their running watts for a second or two when they start. The calculator adds the single largest startup surge to the running watts of everything else, then adds a safety margin (default 20%) so the unit is never maxed out.
Typical running and startup watts below are industry averages. Always confirm the exact numbers on your appliance nameplate before buying — a label that reads 1,200 running / 2,200 starting changes the answer.