A typical house needs anywhere from about 5,000 watts to 20,000 watts of generator capacity, depending on how much of the home you want to run and which appliances you include. To pick the right size, you add up the wattage of the circuits or appliances you want powered during an outage, including their higher “starting” watt loads, then choose a generator with a bit of extra capacity for safety.

How big of a generator to run a house?

For most detached single-family homes:

  • Around 5,000–7,500 watts can usually cover “essentials only” (fridge, lights, a sump pump, small HVAC or furnace blower, Wi‑Fi, some outlets).
  • Around 7,500–12,000 watts can typically handle essentials plus more convenience loads, and maybe a small central AC or well pump if managed carefully.
  • Around 14,000–22,000 watts (a true whole‑house standby generator) can often run nearly everything in a typical 2,000–3,000 sq ft home, including central AC, if sized correctly by a pro.

The exact size depends less on square footage and more on:

  • How many big 240‑volt loads you have (central AC, electric range, electric dryer, well pump, electric water heater, hot tub, EV charger).
  • Whether you want “survival mode” (heat, some lights, fridge) or “almost normal life” (cooking, laundry, full HVAC, etc.).

Simple sizing steps (DIY estimate)

You can get a decent estimate with this quick process (always confirm with an electrician before buying):

  1. List essential circuits/appliances
    • Examples:
      • Refrigerator or two
      • Furnace blower or boiler pump
      • Sump pump / well pump
      • A few lighting circuits
      • Wi‑Fi, phone chargers, TV/computer
      • Possibly a small window AC or one central AC unit
    • Decide if you want to add “comfort” loads like a microwave, some kitchen outlets, or a small AC.
  1. Find running and starting watts
    • Look on appliance labels or manuals for watts or amps.
    • If you only see amps, multiply amps × volts (120 or 240) to approximate watts.
    • Motors (fridge, pumps, AC, compressor) often need 2–3× their running watts to start.
  1. Add them up and add a safety margin
    • Add all the running watts for devices you might have on at the same time.
    • Add extra for starting watts of the largest motor loads (often listed as “starting” or “surge” watts).
    • Add a 20–25% buffer so your generator isn’t at its limit all the time.
  1. Match to generator size “bands”
    • If your total (with buffer) is around:
      • 3,500–5,000 W: small portable inverter or portable generator.
      • 5,000–7,500 W: larger portable or small “whole‑home” via a transfer switch, running essentials only.
      • 8,000–12,000 W: big portable or small standby generator, running most of the home with some load management.
      • 14,000–22,000+ W: automatic standby generator likely paired to your panel, for near full‑home coverage.

Portable vs whole‑house (standby)

Different generator types change what “how big” feels like in real life.

  • Portable generators (usually 3,000–10,000 W)
    • Good for essentials and some comforts.
    • Need manual setup: wheel it out, fuel it, plug into a transfer inlet or extension cords.
* Usually gasoline or propane; runtime and storage become important.
  • Inverter generators (often 2,000–7,500 W)
    • Quieter and more fuel‑efficient, better for electronics.
    • Ideal if you only need a few circuits and want less noise in a neighborhood.
  • Standby (whole‑house) generators (around 10,000–26,000+ W)
    • Permanently installed outdoors, run on natural gas or propane.
    • Turn on automatically during an outage and can be sized for nearly full‑home use.
* Higher upfront cost but more seamless and “hands‑off.”

Safety, code, and pro help

Even if you rough‑size it yourself, bringing in a licensed electrician or generator installer is critical:

  • They can calculate your home’s actual electrical load (including 240‑V circuits) and recommend the correct generator size and a transfer switch that meets code.
  • A transfer switch or interlock is required to safely connect a generator to your panel and prevent dangerous “backfeeding” into the utility lines.
  • They can also set up load‑shedding modules for standby generators so that big loads (like multiple AC units) cycle rather than all hitting at once.

Quick HTML table: rough sizing guide

html

<table>
  <thead>
    <tr>
      <th>Use level</th>
      <th>Typical watt range</th>
      <th>What it can usually run</th>
    </tr>
  </thead>
  <tbody>
    <tr>
      <td>Essentials only</td>
      <td>5,000–7,500 W [web:6][web:9]</td>
      <td>Fridge, lights, furnace blower, Wi‑Fi, a few outlets, maybe a small window AC or well pump with care [web:5][web:7]</td>
    </tr>
    <tr>
      <td>Comfortable partial house</td>
      <td>7,500–12,000 W [web:4][web:9]</td>
      <td>Essentials plus more rooms, microwave, possibly one small central AC or well pump with smart load management [web:3][web:5]</td>
    </tr>
    <tr>
      <td>Near full‑house</td>
      <td>14,000–22,000+ W [web:3][web:10]</td>
      <td>Most circuits in a typical 2–3 bedroom home, including central AC and major appliances, usually via standby generator [web:3][web:10]</td>
    </tr>
  </tbody>
</table>

Information gathered from public forums or data available on the internet and portrayed here.