Updated Jan 31, 2026
Whole House Generator Calculator
Size a whole house generator with a fast quiz or a detailed load list. See running watts, surge demand, and a recommended kW range with buffer.
Reviewed by SuperCalc Engineering
Sizing inputs
Extra load (optional)
Recommended size
Quick quizSend your request or a correction and we'll review it within 24 hours.
You can also use the Feedback button in the bottom-right corner.
How this calculator works
We estimate your running load, add surge allowance for motor starts, then apply a safety buffer to suggest a practical generator size range.
The quick quiz is fast for planning, while the load list is best for accurate sizing.
Whole house generator sizing tips
- High-surge loads (AC, well pumps) drive generator size more than small appliances.
- Electric heat and EV charging can push sizing into 20-30 kW ranges.
- Load management can reduce required kW by staggering startup loads.
Example result snapshot
FAQ
What size whole house generator do I need?
Most homes fall in the 12-24 kW range, but the right size depends on your HVAC, electric appliances, and whether you back up the whole home or just essentials.
How does this sizing calculator work?
It estimates running load, adds a surge allowance for motor starts, then applies a safety buffer to recommend a practical generator size.
Is a load list more accurate than a quick quiz?
Yes. A full load list is the most accurate way to size a generator. The quick quiz is a fast estimate to narrow the kW range.
Do I need a load management module?
If your surge demand is high or you want to keep generator size smaller, load management can stagger large appliances like AC or electric dryers.