Generator Sizing Calculator

Choose the appliances you need to keep running during an outage and get a recommended backup generator size that covers both continuous load and startup surge.

Appliances to Power

Enter how many of each appliance you want to run at once. Leave blank or 0 to skip.

Refrigerator

700 W running / 2,200 W surge each

Sump pump

800 W running / 2,000 W surge each

Furnace blower

800 W running / 2,350 W surge each

Window AC

1,200 W running / 1,800 W surge each

Well pump

1,000 W running / 3,000 W surge each

Microwave

1,000 W running / 1,000 W surge each

Lights (10-bulb group)

500 W running / 500 W surge each

Space heater

1,500 W running / 1,500 W surge each

Other running watts (optional)

Additional continuous watts not listed above

Recommended Size

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Select the appliances you want to run to see a recommended generator size

How Generator Sizing Works

Running vs. Surge Watts

• Running (rated) watts are the continuous power a device needs
• Surge (starting) watts are the brief spike when a motor kicks on
• Motors like pumps and compressors surge well above their running draw
• Usually only one large motor starts at a time

How We Size It

• Add up the running watts of everything you select
• Add the single largest startup surge on top of that
• Include roughly 20% headroom so the generator is not maxed out
• Round up to a common generator size

Wattage presets are typical estimates. Check the nameplate on your own appliances for exact figures, and consult a licensed electrician before connecting a generator to your home.

Generator Sizing Calculator

Appliances to Power

Recommended Size

Sizing Note

How Generator Sizing Works

Running vs. Surge Watts

How We Size It

Recommended gear for this tool

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