Motors and compressors need a short burst of extra power to start. Enter your appliance's running watts to estimate its surge requirement, or add several to find your system's total surge need.
Your generator or inverter's surge rating must exceed this number even briefly, or the appliance can trip its protection or fail to start.
Generators and inverters are rated for both continuous (running) and surge (starting) watts, and it's almost always the surge number that determines whether an appliance starts at all. Undersizing for surge is the single most common generator-sizing mistake — check this against your generator backup calculator results before buying.
Anything with a compressor or large motor — air conditioners, well pumps, and refrigerators typically spike 3-5× their running wattage for under a second at startup.
Only the single highest surge matters if appliances start one at a time — but if two might start simultaneously (like a fridge and AC on the same circuit), add their surges together for a safe margin.