How it works
Peak watts are running watts plus the extra starting surge: peak = running watts + surge extra watts. The recommended size adds a 20% headroom margin on top of peak: recommended = peak × 1.20. For example, 2,750 W running plus 2,000 W surge extra is 4,750 W peak, and 4,750 × 1.20 = 5,700 W recommended. The margin leaves room for surges and for loads that were not counted exactly.
Frequently asked questions
What is starting surge?
Many motors briefly draw far more power when they start than when they run. That short spike is the surge. If you ignore it, a generator can trip or stall the moment a motor starts.
Why add 20% headroom?
It is a simple safety margin in this calculator, not a manufacturer's rating. It helps cover estimation error, but it does not replace the generator maker's own sizing guidance.
Should I count every appliance in the house?
No — count only what you plan to run at the same time on the generator. Counting everything at once will oversize the result; leaving out a large motor will undersize it.