What size generator do you actually need?

Check what you want to power. The plate below computes running watts, worst-case starting surge, and the size to buy — including the 25% headroom every load calculation should carry.

How the math works

Every motor-driven appliance (anything with a compressor or pump) briefly draws far more at start-up than while running. A refrigerator that runs at 300W can demand 1,500W for the half-second its compressor spins up. Sizing means covering two numbers: the sum of running watts for everything at once, and the largest single start-up surge stacked on top of that sum, since your biggest motor can kick in at any moment.

We add 25% headroom to the running total because generators shouldn't live at their limits: continuous full-load running shortens engine life, wastes fuel, and leaves nothing for the load you forgot.