Generator Sizing Calculator: What Size Generator Do I Need?

Understanding Generator Sizing

Generator sizing is based on two key measurements: running watts and starting watts (also called surge watts). Running watts represent the continuous power needed to keep appliances operating, while starting watts account for the initial surge of power needed when motors start up.

Common high-surge appliances include air conditioners, well pumps, sump pumps, and refrigerators. These can require 2-3 times their running wattage just to start. Our calculator accounts for these surge requirements automatically.

For more guidance on safe generator operation, check out our generator safety tips guide.

Portable vs. Standby Generators

• Portable Generators: Ideal for powering essential circuits during outages. More affordable upfront, requires manual setup and refueling. Best for homes needing under 10,000 watts.
• Standby Generators: Permanently installed, automatically starts during power outages, runs on natural gas or propane. Higher upfront cost but provides whole-home backup power and convenience.