Panel Headroom Independent tools for home electrical decisions

Calculator

Generator size calculator

Add the running watts of loads that may run at the same time, then add only the single largest starting increment. Default wattages are Honda’s published approximations, retrieved 2026-11-11.

Source: Honda Power Equipment, “What wattage generator do I need?” Home Applications table. Enter a nameplate whenever you have one.

Check every load you might run together during an outage. Do not add all of the starting watts together. Honda’s published method — and the usual portable-generator worksheet — is to total running watts, then add the extra starting watts of the single hardest-starting load.

Add a nameplate (for loads Honda does not list)

Well pumps, central heat pumps, and many other motors are not in Honda’s home table. Use the nameplate running watts and the listed starting watts or locked-rotor current × volts. We do not invent a default.

Related questions

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.