Generator Size Calculator
Watts needed to run your home.
Enter your values
Results update instantly as you type — no submit needed.
Results
- Minimum generator size
- 8,000 W
- Running watts
- 4,200 W
- Peak demand
- 6,400 W
- Fuel needed
- 9 gallons
- In kilowatts
- 7.68
Quick answer
Size a generator on total running watts plus the largest single starting surge, then add 20% headroom.
How to use the Generator Size Calculator
- 1Add the running watts of everything you need.
- 2Find the largest single starting surge (usually a fridge or pump).
- 3Add 20% headroom.
Frequently asked questions
What are typical loads?
Fridge 700 W running, sump pump 800 W, window AC 1200 W, furnace fan 800 W.
Do I need a transfer switch?
Yes for hardwired circuits — never backfeed through an outlet.