What Size Generator Do I Need for My House? (Chart)
A quick-reference generator sizing chart — match your home size and the appliances you want to back up to a recommended running-watt total and standby kW class.
This generator sizing chart maps common backup scenarios to the running watts they need and the generator size that covers them. Find the row that matches what you want to keep on, then pick a generator whose rated watts (or kW) meets or beats it with some headroom. For an exact figure tailored to your appliances, use the generator sizing calculator.
Generator size chart by scenario
| Scenario | Running watts | Recommended size |
|---|---|---|
| Fridge + a few lights | 1,500–2,500 W | 3,000 W inverter |
| Fridge, freezer, lights, Wi-Fi | 2,500–3,500 W | 3,500–4,000 W |
| Essentials + furnace + a pump | 5,000–7,500 W | 7,500 W portable |
| Essentials + a window AC | 7,500–9,500 W | 9,500 W dual-fuel |
| Most of a mid-size home | 10,000–13,000 W | 12,500 W / 14 kW standby |
| Whole house, one central AC | 16,000–22,000 W | 20–22 kW standby |
| Large home, multiple AC / electric heat | 22,000–26,000 W+ | 24–26 kW standby |
Appliance wattage chart
Add up the appliances you want to run at once. Motors also need a starting surge — the biggest one sets the peak.
| Appliance | Running watts | Starting watts |
|---|---|---|
| Refrigerator / freezer | 700 | 2,200 |
| Standalone chest freezer | 500 | 1,500 |
| Furnace blower (gas, ½ HP) | 800 | 2,350 |
| Well pump (½ HP) | 1,000 | 3,000 |
| Sump pump (⅓ HP) | 800 | 2,000 |
| Window AC (10,000 BTU) | 1,200 | 3,600 |
| Central AC (3-ton) | 5,000 | 15,000 |
| Electric water heater | 4,500 | 4,500 |
| Microwave | 1,000 | 1,000 |
| Lights (10 × LED) | 400 | 400 |
How to use the chart
- Add the running watts of everything you want on at once.
- Add the single largest starting surge from the list.
- Add about 20% headroom and round up to the next generator size.
Prefer to skip the math? The sizing calculator does all three steps as you check boxes, and the whole-house sizing guide walks through a full home.
These are planning figures; your appliances may vary. A whole-house standby install must be sized and wired by a licensed electrician.
Frequently asked questions
How do I read a generator sizing chart?
A generator sizing chart maps a scenario — essentials only, a mid-size home, or a whole house with central AC — to a recommended running-watt total and a generator size. Find the row that matches what you want to back up, read across to the running watts, and pick the generator whose rated watts (or kW) meets or beats it with some headroom. A chart is a starting point; for an exact figure, add your own appliances in the calculator.
What size generator do I need for my house?
It depends on the load: essentials (fridge, furnace blower, a pump, lights) need about 5,000–7,500 running watts; a mid-size home with some comfort loads needs 7,500–10,000 watts; a whole house with central AC needs an 18–26 kW home standby. The chart on this page shows these tiers, and the sizing calculator turns your exact appliance list into a number.
How many watts to run a house?
A typical house draws roughly 5,000–7,500 running watts for essentials and 15,000–25,000 watts (15–25 kW) to run everything including central air conditioning. The exact figure depends on your appliances and how many run at once. Remember to allow for starting surges — motors briefly pull two to three times their running watts — which is why generators are sized above the steady load.