WattSizer

Generator and backup-power sizing for refrigerators, sump pumps, well pumps, RV AC, CPAP machines, tools, and outage essentials.

Refrigerator and freezerCPAP overnightRV AC on 3500 W

Never operate a fuel-burning generator indoors, in a garage, on a porch, or near open windows. Use a listed transfer switch or interlock installed by a qualified electrician for home wiring, and verify actual device nameplates before buying equipment.

Start with a common outage load

Running load0 W
Starting load0 W

Recommended generator0 W
LoadRunning wattsStarting watts

Power station estimate

For battery units, the selected running load needs about 0 Wh for 8 hours or 0 Wh for 12 hours before weather, battery age, and inverter losses.

Safety check

Never operate a fuel-burning generator indoors, in a garage, on a porch, or near open windows. Use a listed transfer switch or interlock installed by a qualified electrician for home wiring, and verify actual device nameplates before buying equipment.

Popular sizing questions

What size generator for a refrigerator and freezer?
Home EssentialsWhat size generator for a sump pump and refrigerator?
Storm PrepWhat size generator for a well pump?
Well PumpWhat size generator for a furnace and refrigerator?
Winter OutageWill a 3500 watt generator run an RV AC?
RvWill a 4000 watt generator run a 15,000 BTU RV AC?
RvPortable power station size for CPAP overnight
MedicalPortable power station for CPAP with humidifier overnight
MedicalApartment outage generator alternatives for fridge, router, and lights
ApartmentGenerator size for a small food truck prep setup
Food TruckWhat size generator for garage freezer and sump pump?
Storm PrepBackup power size for oxygen concentrator and phone
Medical