Generator Size Calculator
Calculate what size generator you need.
Add your appliances and their wattages to see total running and startup watts required.
Recommended Generator Size
Generator sizing requires knowing both running watts and startup (surge) watts.
Total Running Watts = Sum of all appliance running wattages
Total Startup Watts = Running Watts + Largest single startup surge
Motor-driven appliances (refrigerators, AC units, pumps) need 2–3× their running watts to start up. This surge lasts only a few seconds but the generator must handle it.
Common appliance wattages (running / startup):
- Refrigerator: 150 W / 400 W
- Sump pump (1/2 HP): 800 W / 2,000 W
- Window AC (10,000 BTU): 1,200 W / 3,600 W
- Central AC (3 ton): 3,500 W / 7,000 W
- Microwave: 1,000 W / 1,000 W (no surge)
- LED lights (10 bulbs): 100 W / 100 W
- Well pump (1/2 HP): 1,000 W / 2,500 W
- Space heater: 1,500 W / 1,500 W
- TV and router: 200 W / 200 W
Generator size recommendations:
- 3,000–4,000 W: Essential circuits only
- 5,000–7,500 W: Most home essentials
- 10,000–12,000 W: Nearly full-home backup
- 20,000+ W: Whole-house standby
Enter appliances as: name, running watts, startup watts (one per line)