Generator sizing — motors demand far more to start than to run
Motors draw 2–3× their running watts for the moment they start. Size to running total + the single largest surge, × 1.25 headroom.
What this diagram shows
Bar chart comparing running watts to starting watts for three common backup loads: a chest freezer runs at 500 watts but starts at 1,500, a 1 HP well pump runs at 2,000 watts but starts at 4,000, and a 3-ton central air conditioner runs at 3,500 watts but starts at 8,500. The sizing method: total the running watts of everything on simultaneously, add the single largest starting surge, then add 25 percent headroom so the generator runs near 80 percent of capacity.
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Generator Size Calculator
What size generator do you need? Free calculator from the loads you want to back up — running watts, motor-starting surges, and sizing headroom.
