Match the inlet to the largest generator you reasonably expect to plug in, and remember the watt arithmetic: 30 A × 240 V = 7,200 W, and 50 A × 240 V = 12,000 W. Those are circuit limits, not a promise that your generator can produce that much. A common r/Generator piece of advice is that a larger inlet is acceptable if the generator’s own breaker is the protection; feeding a smaller house inlet from a larger generator outlet is the direction that goes wrong if it is improvised.
If you only need a fridge, a furnace blower and lights (about 2,300 starting watts in the Honda-based essential-load example), a 30-amp inlet can be electrically sufficient. If you hope to run central air, a 50-amp inlet is often the better installation even before you buy the larger generator, because changing an inlet later is more work than buying a bigger inlet now.
This is not a DIY wiring diagram. A licensed electrician should size the inlet, the generator breaker in the panel, and the cord, and should install a listed interlock or transfer switch. Use the calculator to see which side of 7,200 W your load list sits on.
This is not a permit calculation, a utility approval, or a substitute for a licensed electrician, HVAC contractor, or the authority having jurisdiction. Panel Headroom is an independent educational site. It is not a utility, a certification body, or a contractor. Electrical and generator work that is done incorrectly can cause fire, shock, or carbon monoxide poisoning. Use the adopted electrical code and manufacturer instructions; pull permits where required.