Generator calculator
Generator Sizing Calculator
Estimate standby generator kW from appliance running watts and the largest starting wattage burst before an electrician performs the load calculation.
Screening estimate only.These calculators use only the values you enter. A licensed electrician's load calculation is authoritative before equipment is selected or installed.
Screening result
Fine Print and Sources
Screening estimate only. These tools use only the values you enter and simple planning math. A licensed electrician's load calculation is authoritative for equipment selection, transfer equipment, permitting, fuel piping, and final installation scope.
The sizing tool follows Generac's planning formula: total watts equals the sum of running wattages plus the highest single starting wattage burst, then divide by 1000 for kW. Norwall recommends about 25 percent added capacity margin, and motor starting wattage is often 2 to 3 times running wattage.
- Generac generator sizing guide: cites running wattage, starting wattage, essentials guidance, professional load analysis, and the whole-home 22 kW planning anchor.
- Norwall standby generator sizing guide: cites the 25 percent headroom recommendation and motor starting load guidance.