Generator sizing calculator

Tick appliances, edit running and starting watts, choose a startup assumption, and add a buffer. The default formula is largest single surge plus already-running loads.

Editable calculator

Running load0 W

Starting load0 W

Recommended generator0 W

Startup assumption Buffer: 20%

Load	Running watts	Starting watts
Refrigerator
Upright freezer
Chest freezer
Mini fridge
1/3 hp sump pump
1/2 hp sump pump
1/2 hp well pump
1 hp well pump
Gas furnace blower
Oil furnace burner and blower
Pellet stove
5,000 BTU window AC
10,000 BTU window AC
13,500 BTU RV AC
15,000 BTU RV AC
1,000 W microwave
Coffee maker
Toaster
Electric kettle
Ten LED lights
Router and modem
Wi-Fi mesh node set
55 inch LED TV
Laptop charger
Four phone chargers
Box fan
Dehumidifier
CPAP without heated humidifier
CPAP with heated humidifier
Oxygen concentrator
Nebulizer
Power wheelchair charger
Garage door opener
Washing machine
Gas dryer motor
Electric pressure cooker
Single induction hot plate
Two tool battery chargers
Circular saw
Miter saw
Table saw
Small air compressor
Shop vacuum

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.

Formula

running watts = sum(selected running watts)

starting watts = max(single starting watts + other running watts)

recommendation = round up(max(running, starting) x (1 + buffer))