Generator Wattage Guide: How Many Watts Do I Need?

Two numbers matter when sizing a generator: running watts (what an appliance draws continuously) and surge watts (the brief spike when a motor starts — often 2-3x the running wattage). A generator needs enough surge capacity to start your largest motor while everything else is already running.

Common approximate running watts: refrigerator ~700W, sump pump ~800W, furnace fan ~600W, well pump ~1,000W, window AC ~1,200W, central AC ~3,500W. Add these up for your must-run list, then check the surge rating of whichever appliance has the largest motor.

A generator's rated (running) watts must cover your total running load; its surge/peak watts must cover your running load minus the largest single motor's running watts, plus that motor's surge watts.

Our generator sizing calculator does this math for you — check off your appliances and it estimates a sized-to-fit tier.