Don't guess on your generator size. Use our free generator size calculator to calculate exact running watts, starting surge wattage, kW, kVA, and amps for home backup, RVs, emergency power, or standby generators.
1. Select Household Appliances
Choose from refrigerators, central air conditioners, sump pumps, lights, and heaters to calculate total continuous running watts.
2. Calculate Starting Surge Watts
Motor-driven appliances require 2x to 4x their running wattage during startup. We automatically add the highest starting surge requirement.
3. Recommended Generator Size
Includes a recommended 20% safety capacity margin to protect engine efficiency, prevent overload trips, and ensure clean voltage output.
Whole House Generator Sizing by Square Footage
| Home Size |
Essential Circuits Only |
Essentials + Central AC (with Soft Start) |
Full Whole-House Standby |
| 1,000 – 1,500 sq ft (2 Bed) | 3,500 – 5,000 W | 6,500 – 8,000 W | 10,000 – 14,000 W |
| 1,600 – 2,400 sq ft (3-4 Bed) | 5,500 – 7,500 W | 8,500 – 11,500 W | 16,000 – 20,000 W |
| 2,500 – 3,500 sq ft (4-5 Bed) | 7,500 – 9,500 W | 12,000 – 15,000 W | 22,000 – 24,000 W |
| 3,600+ sq ft (5+ Bed / Dual AC) | 9,500 – 12,000 W | 18,000 – 22,000 W | 26,000 – 48,000+ W |
Standard Generator Sizing Guidelines
- 2,000 – 3,000 Watts: Ideal for RV camping, tailgating, small electronics, TV, mini-fridge, and LED lighting.
- 3,000 – 5,000 Watts: Small home emergency backup. Powers refrigerator, freezer, sump pump, lights, and microwave.
- 5,000 – 8,500 Watts: Medium home backup. Powers well pump, furnace blower, refrigerator, lights, and small window AC unit.
- 8,500 – 12,000 Watts: Heavy-duty portable generator with transfer switch. Powers central AC (up to 3-ton with soft start), well pump, and essential home circuits.
- 14,000 – 24,000+ Watts: Whole house standby automatic generator. Powers entire home seamlessly including central air, electric water heater, stove, and clothes dryer.
Common Household Appliance Wattage Chart
| Appliance |
Running (Continuous) Watts |
Starting (Surge) Watts |
| Refrigerator / Freezer | 700 W | 2,200 W |
| Central AC (3-Ton / 36,000 BTU) | 3,500 W | 10,500 W |
| Sump Pump (1/2 HP) | 1,050 W | 2,150 W |
| Well Pump (1/2 HP) | 1,000 W | 2,100 W |
| Furnace Blower Fan (1/2 HP) | 800 W | 2,300 W |
| Microwave Oven | 1,000 W | 1,000 W |
| Electric Water Heater | 4,500 W | 4,500 W |
| Portable Space Heater | 1,500 W | 1,500 W |
| Wi-Fi Router & Modem | 20 W | 20 W |
| LED Lights (10 Bulbs) | 100 W | 100 W |
Explore Specialized Generator & Electrical Calculators