What Size Generator Do I Need for My House? (Wattage Chart)

Wattage data last verified 2026-08-28 · every wattage cites its source · methodology

It depends on how much of the house you back up: essentials run ~4,700W (fridge, sump pump, 1/3-hp furnace blower, lights, phones, router), a comfort setup ~9,600W, and near-whole-home coverage ~27,900W — sized as running watts + the largest startup surge + 20% headroom, from the sourced chart below.

The list, with sourced watts

ApplianceRunning wattsStarting (surge)
Refrigerator/freezer (standard household)1,0002,200
Chest / deep freezer7201,890
Sump pump (1/3 HP)8002,100
Well pump (1/2 HP)1,0002,100
Furnace fan blower (1/2 HP)1,1002,350
Window AC (10,000 BTU)1,2002,000
Microwave oven (1000 W cook power)1,0002,000
LED light (per bulb/fixture, 60W-equivalent class)13—
TV, LED flat-screen190—
Wi-Fi router + modem20—
Cell phone charger25—
Coffee maker1,200—
Washing machine1,1503,450
Electric water heater (40-gal tank)5,500—
Central AC (36,000-40,000 BTU / 3+ ton)6,0007,200
Running watts versus starting surge, per appliance Horizontal bars for 15 appliances. The solid bar is running watts; the lighter extension is the extra the motor briefly demands at startup. Refrigerator/freezer 1,000 running, 2,200 starting. Chest / deep freezer 720 running, 1,890 starting. Sump pump 800 running, 2,100 starting. Well pump 1,000 running, 2,100 starting. Furnace fan blower 1,100 running, 2,350 starting. Window AC 1,200 running, 2,000 starting. Microwave oven 1,000 running, 2,000 starting. LED light 13 running. TV, LED flat-screen 190 running. Wi-Fi router + modem 20 running. Cell phone charger 25 running. Coffee maker 1,200 running. Washing machine 1,150 running, 3,450 starting. Electric water heater 5,500 running. Central AC 6,000 running, 7,200 starting. running watts extra at startup Refrigerator/freezer 1,000 → 2,200W Chest / deep freezer 720 → 1,890W Sump pump 800 → 2,100W Well pump 1,000 → 2,100W Furnace fan blower 1,100 → 2,350W Window AC 1,200 → 2,000W Microwave oven 1,000 → 2,000W LED light 13W TV, LED flat-screen 190W Wi-Fi router + modem 20W Cell phone charger 25W Coffee maker 1,200W Washing machine 1,150 → 3,450W Electric water heater 5,500W Central AC 6,000 → 7,200W
The startup surge is the part a generator has to cover but a spec sheet rarely leads with — here the washing machine briefly demands 2,300W more than it runs on. Same figures as the table, each cited on the methodology page.

Essentials — ~4,700W

fridge, sump pump, 1/3-hp furnace blower, lights, phones, router

2,558W running + 1,300W largest surge = 3,858W → × 1.2 = ~4,700W
Westinghouse WGen5300
5,300W rated · 6,600W starting · gasoline
Spec: manufacturer

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Honda EU7000iS
5,500W rated · 7,000W starting · gasoline (EFI) · inverter
Spec: authorized_dealer

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Comfort — ~9,600W

essentials + freezer, well pump, window AC, microwave, TV

6,668W running + 1,300W largest surge = 7,968W → × 1.2 = ~9,600W
Westinghouse WGen9500DF
9,500W rated · 12,500W starting · dual fuel (gasoline/propane)
Spec: manufacturer

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DuroMax XP13000EH
10,500W rated · 13,000W starting · dual fuel (gasoline/propane)
Spec: manufacturer

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Near-whole-home — ~27,900W

everything on this page at once, incl. central AC, washer and electric water heater

20,918W running + 2,300W largest surge = 23,218W → × 1.2 = ~27,900W

No unit in our verified catalog cleanly covers this load — see the calculator to adjust your list.

The arithmetic

Running total: 20,918W
+ largest single starting surge: 2,300W
= peak demand: 23,218W
× 1.2 headroom → recommended rating: ~27,900W

Adjust this list in the calculator →

What size generator do I need for my house?

Essentials ~4,700W; comfort ~9,600W; near-whole-home ~27,900W. Size to the loads you actually run at once, not the house.

Can I size a generator by square footage?

No. Generators size by electrical load, not floor area — a small house with a well pump and electric water heater needs more than a large house on gas. Add up your actual appliances.

Why do starting watts matter?

Motor-driven appliances briefly draw 2–4× their running watts at startup. Cover the running total plus the single largest surge, or the motor stalls.

Sources

Figures are conservative sizing values chosen from the range these sources report. Your appliance's nameplate is authoritative.