Generator Wattage Calculator

Running watts (also called rated watts) are the continuous power an appliance needs to operate. Surge watts (starting watts) are the brief spike of power required to start motor-driven appliances like refrigerators, air conditioners, and pumps — typically 2–3× the running wattage. Your generator must handle both, so always size it to cover the highest surge load you expect.

Add up the running watts of everything you want to power simultaneously. Then identify the appliance with the highest surge wattage and add that surge on top of the total running watts. The result is the minimum generator output you need. It's wise to add a 10–20% buffer so the generator isn't running at full capacity continuously.

Yes, but central AC units are among the most demanding loads — typically 2,000–4,000W running with surges up to 6,000W or more. You'll need a generator rated at least 7,000–10,000W if you want to run central AC alongside other appliances. Window units are a more generator-friendly alternative.

Focus on health and safety essentials first: refrigerator (to prevent food spoilage), sump pump (to prevent flooding), heating or cooling equipment, medical devices, and lighting. Once those loads are covered, add other appliances within the remaining generator capacity.

Electric motors require a large burst of current to overcome inertia and get spinning. Once running, the current drops to a steady level. This starting surge typically lasts less than a second, but the generator must be rated to supply it or it will stall, trip a breaker, or sustain damage.

No. Generators produce carbon monoxide (CO), an odorless, colorless gas that is lethal in enclosed spaces. Always operate a generator outdoors, at least 20 feet from windows, doors, and vents. Never run one in a garage, even with the door open.

Most experts recommend choosing a generator rated 10–25% higher than your calculated load. This prevents the engine from running at maximum output continuously, which reduces wear, improves fuel efficiency, and extends the generator's service life.

Typical running wattages: refrigerator ~150–200W, window AC ~1,200W, central AC ~2,000–4,000W, electric water heater ~4,500W, electric dryer ~5,400W, microwave ~1,000W, washing machine ~1,150W, LED lighting ~60W per 10 bulbs, TV ~150W, laptop ~50–150W. Always check your appliance's nameplate for exact figures.