Emergency Generator Calculator
Plan for critical power outages. Select essential survival appliances, medical equipment, sump pumps, and heating systems to accurately size an emergency backup generator.
Recommended Size
0 W
Safety Tip
Never run a generator indoors or in a garage. CO gas kills. Keep generators 20ft away from windows.
Emergency Generator Sizing Chart & Formulas
Refer to this essential wattage guide for critical home survival loads during power outages, including medical devices, refrigeration, water pumps, and space heating.
Core Sizing Formulas
P_run = Σ P_running_i
Sum of continuous running wattage for all operating appliances.
P_surge = max(P_start_i - P_run_i)
Highest individual motor starting surge delta added to continuous load.
P_gen = (P_run + P_surge) × 1.20
20% buffer prevents voltage dips and generator overload trips.
Amps = Total Watts ÷ 120V
Calculates required receptacle and wire circuit breaker amp rating.
| Essential Appliance | Category | Running Watts | Starting Watts | Surge Factor | Rec. Generator Size |
|---|---|---|---|---|---|
| Sump Pump (1/3 HP) | Water & Drainage | 800 W | 1,300 W | 1.6× | 2,000 W |
| Sump Pump (1/2 HP) | Water & Drainage | 1,050 W | 2,150 W | 2.0× | 3,500 W |
| Well Pump (1/2 HP) | Water Supply | 1,000 W | 2,100 W | 2.1× | 3,500 W |
| Well Pump (1 HP) | Water Supply | 2,000 W | 4,000 W | 2.0× | 6,500 W |
| Refrigerator / Freezer Critical | Refrigeration | 700 W | 2,200 W | 3.1× | 3,000 W |
| Chest Freezer | Refrigeration | 500 W | 1,500 W | 3.0× | 2,000 W |
| Microwave Oven (1000W) | Kitchen | 1,500 W | 1,500 W | 1.0× | 2,000 W |
| Coffee Maker (Drip) | Kitchen | 1,000 W | 1,000 W | 1.0× | 1,200 W |
| Electric Range (1 Element) | Kitchen | 1,500 W | 1,500 W | 1.0× | 2,000 W |
| Electric Water Heater | Water Heating | 4,000 W | 4,000 W | 1.0× | 5,000 W |
| Washing Machine | Laundry | 500 W | 1,200 W | 2.4× | 1,500 W |
| Electric Clothes Dryer | Laundry | 5,400 W | 5,400 W | 1.0× | 7,000 W |
| CPAP Machine Medical | Medical | 60 W | 60 W | 1.0× | 500 W |
| Oxygen Concentrator Medical | Medical | 400 W | 600 W | 1.5× | 1,000 W |
| Furnace Fan (1/3 HP) | Heating | 600 W | 1,500 W | 2.5× | 2,000 W |
| Furnace Fan (1/2 HP) | Heating | 800 W | 2,000 W | 2.5× | 3,000 W |
| Portable Space Heater | Heating | 1,500 W | 1,500 W | 1.0× | 2,000 W |
| Window AC (10k BTU) | Cooling | 1,000 W | 2,200 W | 2.2× | 3,000 W |
| Central AC (3 Ton) | Cooling | 3,500 W | 9,000 W | 2.6× | 12,000 W |
| Garage Door Opener (1/2 HP) | Household | 550 W | 1,100 W | 2.0× | 2,000 W |
| LED Lights (10x) + WiFi | Lighting/Comms | 105 W | 105 W | 1.0× | 500 W |
| TV (55") & Entertainment | Electronics | 150 W | 150 W | 1.0× | 500 W |
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