// Calculator

Generator Sizing Calculator

Pick the appliances you need during an outage and get the running watts, the largest starting surge and the generator size that covers both.

Recommended generator3,000 starting watts

Running load820 W

Largest surge+1,500 W

Peak demand2,320 W

Voltage needed120 V

Refrigerator (18-22 cu ft) sets the surge. Over 24 hours this list uses roughly 8.8 kWh, which is the number to use when sizing a battery instead.

Choose what has to run

Numbers are typical planning figures. The data plate on your own appliance always wins.

Kitchen

Refrigerator (18-22 cu ft)700 W / 2,200 W start

Chest freezer500 W / 1,500 W start

Microwave (1000 W)1,200 W

Coffee maker900 W

Dishwasher1,300 W / 1,800 W start

Electric range element2,100 W · 240V

Toaster oven1,100 W

Heating & cooling

Furnace blower (1/2 hp)800 W / 2,350 W start

Furnace blower (1/3 hp)600 W / 1,800 W start

Gas boiler controls & pump300 W / 700 W start

Central AC, 2 ton2,000 W / 5,900 W start · 240V

Central AC, 3 ton3,000 W / 8,500 W start · 240V

Window AC (10,000 BTU)1,200 W / 3,000 W start

Space heater (1500 W)1,500 W

Ceiling fan60 W / 100 W start

Box or pedestal fan100 W / 200 W start

Water

Well pump (1/2 hp)1,000 W / 3,000 W start · 240V

Well pump (1 hp)1,500 W / 4,500 W start · 240V

Sump pump (1/3 hp)800 W / 2,600 W start

Sump pump (1/2 hp)1,050 W / 3,000 W start

Electric water heater4,500 W · 240V

Gas water heater controls100 W

Laundry

Washing machine1,150 W / 2,250 W start

Electric dryer5,400 W / 6,750 W start · 240V

Gas dryer700 W / 1,800 W start

Living & work

LED lighting (10 fixtures)100 W

Television (55" LED)120 W

Wifi router and modem20 W

Laptop65 W

Desktop PC and monitor300 W

Phone and tablet charging30 W

Garage door opener875 W / 2,350 W start

Medical

CPAP, no humidifier40 W

CPAP with humidifier120 W

Oxygen concentrator350 W / 600 W start

Medication refrigerator120 W / 400 W start

Shop & site

Circular saw1,400 W / 2,300 W start

Air compressor (1 hp)1,600 W / 4,500 W start

LED work light100 W

Tool battery charger200 W

How this is calculated

The running total is the sum of every selected appliance at its normal draw. The surge figure is the largest single startup spike on the list, counted as the watts above that appliance's running draw, because motors rarely start at the same instant. Peak demand is the two added together, and the recommendation adds 20 percent headroom and rounds up to the next 500 watts so the engine is not pinned at full load for hours.

Wattage figures are typical planning values, not measurements of your equipment. Always check the data plate, and have an electrician do a code load calculation before buying a whole-home standby unit.