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Quick answer: most homes need a 7,500–10,000 W generator for essentials plus comfort, or 12,000–20,000 W for whole-house backup with central AC. Tick your appliances above — the calculator adds running watts plus the biggest starting surge, adds a 20% safety margin, and recommends a standard size.
What size generator to run a house
Short answer: what size generator to run a house (2.2K searches/month) depends on what you run during an outage. Essentials only (fridge, freezer, furnace blower, sump pump, lights, Wi-Fi): about 5,000–7,500 W. Essentials plus comfort (microwave, TV, window AC): 7,500–10,000 W. Whole house with central AC and electric water heater: 12,000–20,000 W. The calculator above does the exact math for your appliance list.
The sizing formula the pros use: add up the running watts of everything you'll power, add the single highest starting wattage (motors like AC compressors and pumps surge when they kick on), then add a 20% safety margin so the generator never runs flat-out. Round up to the nearest standard size — 3.5, 5, 6.5, 7.5, 10, 12.5, 15, 17.5, 20 or 22 kW.
What size generator to run a 1,500 sq ft house
Short answer: what size generator to run a 1,500 sq ft house (1.0K/month) — a 1,500 sq ft home typically needs 7,500–10,000 W: enough for essentials plus a window AC or microwave, with headroom. Skip the central AC and you can often get by on 5,000–7,500 W.
| Home size | Typical generator size | Covers |
|---|---|---|
| Up to 1,500 sq ft | 5,000–7,500 W | Essentials: fridge, lights, heat, Wi-Fi |
| 1,500–2,500 sq ft | 7,500–12,000 W | Plus well pump, microwave, window AC |
| 2,500–4,000 sq ft | 12,000–20,000 W | Plus central AC, electric range |
| Over 4,000 sq ft | 20,000 W+ | Nearly everything (standby unit) |
What size generator do I need for my house
Short answer: searching what size generator do I need for my house (1.0K/month)? Don't guess from square footage alone — tick your actual appliances in the calculator above. Two 2,000 sq ft homes can differ by 5,000 W depending on electric vs gas heat, well vs city water, and whether the AC runs.
How big of a generator to run a house
Short answer: how big of a generator to run a house (700/month) — in kilowatts: 5–7.5 kW for essentials, 7.5–10 kW for comfort, 12–22 kW for whole-house. When in doubt, size up one step: a generator running at 70% load is quieter, lasts longer, and leaves room for one more appliance.
Frequently asked questions
What size generator do I need to run my house?
Add your running watts, add the highest starting surge, add 20% margin — the calculator above does it automatically. As a rule of thumb: 5,000–7,500 W for essentials, 7,500–10,000 W for comfort, 12,000–20,000 W for whole-house with central AC.
What watt generator do I need to run a house?
Most homes land between 7,500 and 12,000 watts. The exact number is your total running watts plus your biggest motor's starting surge (a central AC can surge to 9,000 W on its own), plus a 20% safety margin.
What size portable generator runs a house?
Portable generators top out around 12,000–15,000 W — enough for essentials and comfort, and some can handle a smaller central AC. For true whole-house backup with central AC plus electric water heater and dryer, you need a 20–22 kW standby unit.
Can I run my whole house on a 7500 watt generator?
A 7,500 W generator runs essentials plus comfort items — fridge, freezer, furnace blower, lights, Wi-Fi, microwave, TV and a window AC. It won't run a central AC together with an electric water heater and dryer; that needs 15,000 W or more.
What is an emergency generator for home use?
An emergency generator for home use is a backup power source — portable (gasoline/propane, 3.5–12 kW, wheeled to where you need it) or standby (permanently installed, 12–22+ kW, auto-starts on outage). Size either type with the calculator above.
Is this generator size calculator free?
Yes — unlimited calculations, free forever. No account, no limits. Everything runs in your browser; nothing is sent to a server.