What Size Generator Do I Need for My House?

Woman with hands held out sitting on a couch in the living room at home with candles burning during a blackout.

If you have ever experienced an extended power outage you already know how frustrating and inconvenient it can be. Well, it can be pretty costly too (when all the food in your refrigerator spoils). So, you have decided it’s time to learn more about a whole house generator, but you’re wondering, “what size generator do I need for my house?”

When it comes to determining the right size generator for your home, it doesn’t mean how much room it takes up in your yard—it means the total wattage required to run your entire home. Determining your specific wattage size requires a bit of math. Don’t panic though! We’ve done most of the homework for you.

What Size Generator Do I Need to Run a House?

Generator sizes are determined by the average wattage use. So, to estimate the appropriate size generator for a home, there are a few ways this can be calculated depending on your needs. You can use the total square footage of your home, your monthly electric usage or breaker size, or you can total up the amount of wattage used by all of your household appliances to determine your wattage requirements.

Keep in mind that having too small or too large of a generator can cause issues. Choosing a size that is too small can ruin your appliances—which defeats the purpose of installing a generator in the first place. Installing a generator that is too big is less efficient and will cost you more to run. It’s best to choose a size that meets your needs now, but has the potential to meet additional power demands later on.

Related Topic: Reasons You Might Want to Install a Generator

Every home is unique when it comes to its specific day-to-day wattage use. When deciding your specific generator size, you need to determine what essentials in your home need to be powered during an outage. Some of those essentials might include: your furnace, A/C, water pump, refrigerator, stove, lighting, office essential, etc. Averaging out the total wattage use of these appliances will give you an estimate on the generator size you need. The wattage use chart below will give you an idea of what size generator you need to power specific appliances.

What Size Generator Do I Need for My House?

Use the chart below to estimate your home’s kilowatt requirements. Add up the wattage of each device in your home; for the most accurate results, check the label or owner’s manual for large appliances and electronics to determine the exact wattage. Once you have the total, divide the sum by 1,000 to calculate the kilowatts you need from your new generator.

Electronics & Appliances 


Central Air Conditioner 


Electric Furnace 


Gas Furnace 


Electric Baseboard Heaters 

225 watts per foot (by heater length) 

Electric Heat Pump 

Up to 15,000 

Water Pump 


Electric Water Heater 


Gas Water Heater 

500 running/1500 starting 



Garage Door Opener 










Gas Dryer 


Electric Dryer 


Washing Machine 




Standalone Freezer 


Electric Oven 


Standby Generators Require Expert Installation 

For many people reliable power is not just a convenience, it’s a necessity. Having a standby generator to keep your home appliances, office and electronics running consistently will provide relief next time the grid goes down. If you have questions, or want more information on how to keep your home up and running when the power goes out, contact the pros at Mr. Electric. We have the knowledge and experience to help you choose the right generator size for your home, and ensure it’s properly installed. Call Mr. Electric today to schedule an appointment.