What Size Whole House Generator Do You Need? Sizing Calculator and Guide
Check off the appliances you need to run during an outage. Get a specific kW recommendation with estimated installed cost. No manufacturer bias pushing the largest model.
Updated 11 April 2026
Quick Sizing by Home Size
A rough starting point. Square footage alone is not enough because two 2,500 sq ft homes can have vastly different electrical loads depending on AC tonnage, whether they have a well pump, and whether heating is gas or electric.
| Home Size | Essentials Only | Whole House (no AC) | Whole House + AC |
|---|---|---|---|
| Under 1,500 sq ft | 10 kW | 14-16 kW | 16-20 kW |
| 1,500 - 2,500 sq ft | 10-14 kW | 16 kW | 22 kW |
| 2,500 - 3,500 sq ft | 14-16 kW | 20-22 kW | 22-25 kW |
| 3,500 - 5,000 sq ft | 16-20 kW | 22-30 kW | 30-48 kW |
| 5,000+ sq ft | 22+ kW | 30-48 kW | 48+ kW |
Interactive Sizing Calculator
Check off every appliance you want to run during an outage. The calculator factors in startup surge and adds 20% headroom.
HVAC
Kitchen
Water
Laundry
General
Other
Recommended Size
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Tip: Load management
A $500-$1,000 load management module can let a smaller generator handle these loads by cycling high-draw appliances instead of running them all at once.
Appliance Wattage Reference
Running watts is what the appliance uses continuously. Startup watts is the surge needed when the motor kicks on. Your generator must handle the highest simultaneous startup surge.
| Appliance | Running Watts | Startup Watts |
|---|---|---|
| Central AC (3-ton) | 3,500W | 7,000W |
| Central AC (5-ton) | 5,000W | 10,000W |
| Electric furnace blower | 500W | 1,500W |
| Refrigerator | 150W | 1,200W |
| Freezer (upright) | 100W | 500W |
| Well pump (1/2 HP) | 750W | 2,200W |
| Well pump (1 HP) | 1,500W | 4,500W |
| Sump pump (1/3 HP) | 800W | 1,300W |
| Electric water heater | 4,500W | 4,500W |
| Gas water heater (elec ignition) | 400W | 400W |
| Washing machine | 500W | 1,200W |
| Electric dryer | 5,400W | 6,000W |
| Dishwasher | 1,800W | 1,800W |
| Microwave (1,000W) | 1,000W | 1,000W |
| Electric range/oven | 3,000W | 3,000W |
| Lights (10 LED bulbs) | 100W | 100W |
| TV (55-inch LED) | 80W | 80W |
| Garage door opener | 550W | 1,100W |
| Security system | 180W | 180W |
| Home office (PC + monitor) | 300W | 300W |
| Medical equipment (CPAP) | 150W | 150W |
| Electric vehicle charger (L2) | 7,200W | 7,200W |
| Hot tub | 6,000W | 6,000W |
| Pool pump (1.5 HP) | 1,500W | 3,000W |
Generator Size Tiers Explained
10 kW
$5,000 - $8,000Small home under 1,500 sq ft. Lights, refrigerator, well pump, sump pump, a few outlets. Cannot run central AC or electric water heater. Good for mild climates where extended outages are rare.
16 kW
$7,000 - $10,000Average home, 1,500-2,500 sq ft. Powers everything except central air conditioning. If you live in a climate where you can open windows during a summer outage, this is the sweet spot for cost versus coverage.
22 kW
$10,000 - $15,000Most popular size. 2,000-3,500 sq ft homes. Powers everything including one standard central AC unit (up to 5-ton). If AC is non-negotiable during outages, this is the right choice.
48 kW+
$15,000 - $25,000Large homes over 4,000 sq ft with multiple AC zones, hot tubs, home workshops, or significant home office loads. Also appropriate for homes with all-electric heating.
Load Management: Smaller Generator, Same Coverage
A load management module ($500-$1,000 installed) lets a smaller generator handle larger loads by intelligently cycling high-draw appliances. Instead of running AC and the dryer simultaneously, it pauses one while the other runs.
Potential Savings
With load management, a 16 kW generator ($7,000-$10,000 installed) can cover the same home that would otherwise need a 22 kW ($10,000-$15,000). That is $1,500-$3,000 in savings after accounting for the load management module cost.
Generac, Kohler, and Cummins all offer compatible load management systems. Generac calls theirs "Smart Management Modules." Kohler calls theirs "Load Control Modules."
Common Sizing Mistakes
Oversizing: wasting $2,000 to $5,000
Buying a 48kW generator for a 2,000 sq ft home. A 22kW handles this with room to spare. Oversized generators burn more fuel during weekly exercise cycles and cost more to maintain. Dealers sometimes push larger models because the margins are higher.
Undersizing: overloading and damaging the unit
A 10kW generator cannot run central AC. Period. Overloading causes the generator to shut down, and repeated overloads damage the alternator. Always size for your actual peak load plus 20% headroom.
Ignoring startup surge
A central AC unit uses 5,000 watts running but needs 10,000 watts to start. If your generator can handle the running load but not the startup surge, the AC will trip the breaker every time it cycles on. Always size for startup watts, not running watts.