Generator size calculator

Choose the appliances you want to run at the same time. The calculator adds their running watts, adds the single biggest starting surge, and suggests a generator size and the power station output and battery you'd need.

Your load

Use + and − to set how many. The link updates as you go, so you can save or share it.

Filter appliances

Type

Backup hours

Refrigerator150 W · start 2,200 W
Space heater1,500 W
Window air conditioner660 W · start 1,500 W
Microwave1,500 W
TV80 W
Sump pump1,000 W · start 2,150 W
CPAP machine22 W
Well pump1,000 W · start 2,100 W
Starlink90 W
Furnace blower500 W · start 1,400 W
Wi-Fi router and modem15 W
LED light bulb9 W
Phone charger15 W
Chest freezer80 W · start 2,200 W
Oxygen concentrator350 W · start 700 W
Electric blanket100 W
Coffee maker1,000 W
Air compressor1,000 W · start 2,000 W
Air fryer1,500 W
Blender700 W · start 1,000 W
Box fan75 W
Ceiling fan50 W
Central air conditioner3,500 W · start 7,000 W
Circular saw1,400 W · start 2,300 W
Clothes iron1,200 W
Computer monitor25 W
Dehumidifier400 W · start 800 W
Desktop computer100 W
Dishwasher1,200 W · start 1,500 W
EV charger7,200 W
Electric clothes dryer5,000 W · start 6,500 W
Electric fireplace1,500 W
Electric kettle1,500 W
Electric oven2,500 W
Electric stove2,000 W
Electric water heater4,500 W
Game console160 W
Gaming PC400 W
Garage door opener875 W · start 2,350 W
Hair dryer1,500 W
Heat pump3,500 W · start 7,000 W
Hot tub4,000 W
Humidifier40 W
Induction cooktop1,800 W
Instant Pot1,000 W
Laptop50 W
Mini fridge80 W · start 400 W
Mini-split920 W · start 1,000 W
Pool pump2,000 W · start 4,000 W
Portable air conditioner1,125 W · start 1,800 W
Portable fridge50 W
Printer15 W
RV air conditioner1,600 W · start 3,000 W
RV water pump50 W
Rice cooker650 W
Slow cooker200 W
Toaster1,100 W
Toaster oven1,500 W
Upright freezer150 W · start 2,200 W
Vacuum cleaner1,000 W · start 1,500 W
Washing machine500 W · start 1,200 W

Running watts: 0 WEverything on at once
Starting watts: 0 WRunning + biggest surge
Generator size: —Pick some appliances
Power station output: —Continuous / surge rating
Battery for 8 h: —Using average draw ÷ 0.85
Amps at 120 V: —Running total ÷ 120

How the calculator sizes a generator

Running watts: we add the typical running watts of everything you pick. This is what the generator must supply continuously.
Starting watts: motors and compressors need a short surge to start. They rarely start at the same moment, so generator makers add only the biggest one. We add the full starting figure on top, which is the cautious way.
Generator size: pick a generator whose running (rated) watts cover the first number and whose starting (peak) watts cover the second.
Power station: its continuous output must cover the running watts and its surge rating the starting watts. Battery size uses the average draw (fridges and freezers cycle on and off) for the hours you choose, divided by 0.85 for losses.

240 V appliances such as well pumps, electric dryers and central AC need a generator with a 240 V outlet and a transfer switch or interlock installed by a licensed electrician. See what size generator do I need for worked examples and running vs starting watts for the why.