Estimate the generator wattage needed for essential loads.
A generator must cover the largest appliance's startup surge, which can be double its running load. Adding a margin gives a safe continuous rating. Generators rated below the startup surge will stall or trip, so sizing past the peak demand prevents failure exactly when you need power.
Generator Size
Size = max(running, largest startup x surge) x (1 + margin)
Size = max(running, largest startup x surge) x (1 + margin) A generator must cover the largest appliance's startup surge, which can be double its running load. Adding a margin gives a safe continuous rating.
Generators rated below the startup surge will stall or trip, so sizing past the peak demand prevents failure exactly when you need power.
This calculator takes 4 inputs: Essential running watts, Largest startup watts, Surge factor, Safety margin. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.