Whole House Generator Size Calculator
Pre-loaded with the appliances a home needs during an outage.
Home backup essentials are pre-checked below
We pre-checked the appliances most homes need during an outage. Adjust the quantities, add or remove devices, then press Calculate. The result shows running watts, the largest motor startup surge, and the generator size that covers it.
Why whole-house sizing is different
A fridge, a well or sump pump and a furnace blower all have motors that surge on start, and a central AC is the single biggest surge on most panels. The calculator assumes only one motor starts at a time, which is the realistic worst case. Add a 20–25% margin if you plan to expand later.
These are typical values — confirm each on its nameplate. A 200-amp panel rarely needs a 200-amp generator; most homes ride through an outage on 5–12 kW of carefully chosen loads.