Home energy · backup planning
Generator sizing, without double-counting surge.
List the loads you want to run together. The estimate adds all running watts, then adds only the largest additional starting-watt allowance.
Load list
Generator requirement
Formula and safety note
Running watts are summed. The minimum surge requirement is running watts plus the largest single additional starting-watt allowance, because motor loads may start while the other listed loads are already running. A 20% running headroom default is an editable planning assumption.
Generac's worksheet uses the same running-plus-highest-starting approach. This is not a wiring, transfer-switch or carbon-monoxide safety plan: follow local code, use outdoor-rated equipment and involve a qualified electrician.