Sizing guideline — confirm with a transfer switch installer

Generator Size Calculator

Check off the appliances you want to keep running during an outage — this adds up their running watts plus the largest single starting surge, since a generator has to handle both at once.

1. Must-Run Appliances

2. Generator Sizing

Running + largest surge

TOTAL RUNNING WATTS

0 W

PEAK WATTS (WITH STARTING SURGE)

0 W

Suggested generator size: Select your must-run appliances to see a suggestion.

Never plug a generator directly into a wall outlet or your panel. Backfeeding can energize utility lines and injure line workers. A permanent generator setup needs a properly installed and permitted transfer switch.

Why starting surge matters

Motors (fridges, sump pumps, furnace blowers, well pumps) draw a short burst well above their running wattage when they first start.
A generator needs enough peak capacity to handle its largest single starting surge on top of everything else already running.
Running multiple large motors on staggered timers, rather than all starting at once, can let you get by with a smaller generator.