Only if the starting watts are the constraint. If the generator already covers both running and starting current from the nameplate, a soft start is optional. If the unit can handle the running load but stalls or trips when the compressor kicks on, owners and technicians often add a listed soft-start kit to reduce locked-rotor demand. It is not a license to undersize the generator, and this site does not claim a standard percentage reduction — that would be inventing a number.
r/Generator posts from 2024–2026 describe exactly this situation: a new 50-amp inlet and a larger generator still could not start the air conditioner until a soft start was installed. Other owners run a 6.5 kW class generator on a four-ton system with a soft start and careful load management. Those are anecdotes, not a sizing table.
Get the nameplate, put running and starting watts in the calculator, and let an HVAC technician say whether a soft-start kit is listed for your outdoor unit. Leave the electric dryer and electric water heater off while the compressor starts.
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.