Generator Size Calculator

Generator sizing is two numbers: running watts (everything on at once) and starting watts — motors like refrigerators, pumps, and AC compressors briefly draw 2–3× their running load when they kick on. Your generator needs to handle the running total plus the single largest start-up surge, with about 10% headroom.

Wattages above are typical values — check the nameplate on your actual appliances. Anything over about 9,500 watts usually means a home standby generator (10–26 kW) with a transfer switch rather than a portable. Never backfeed a panel: use a transfer switch or interlock, installed by an electrician.