How to Size a Generator for Your Home
Choosing the right generator size is one of the most important decisions you will make when investing in backup power. A generator that is too small will overload and shut down when you need it most, while one that is appropriately sized will keep your home running smoothly through any outage. Understanding wattage requirements is the key to getting it right.
Running Watts vs. Starting Watts
Every appliance has two wattage ratings. Running watts (also called rated watts) is the continuous power an appliance needs to operate. Starting watts (also called surge watts) is the brief spike of power required when a motor-driven appliance first turns on. For example, a refrigerator may only need 700 watts to run, but it requires up to 2,200 watts for the compressor to start. Your generator must be able to handle both the total running load and the highest starting surge at any given moment.
Why Slightly Oversizing Is Better Than Undersizing
Our calculator adds a 25% safety margin to your running watts before recommending a generator size. This buffer is intentional and important for several reasons. First, it prevents overloading if multiple appliances start simultaneously. Second, generators that consistently run at near maximum capacity experience more wear and have shorter lifespans. Third, a slight oversizing gives you room to add loads in the future — perhaps an EV charger or a home office setup — without needing a new generator. The cost difference between adjacent generator sizes is typically only a few hundred dollars, making the upgrade well worth the added peace of mind and longevity.
Generator Fuel Types
Standby generators run on natural gas, liquid propane (LP), or diesel. Natural gas is the most popular choice for homes with an existing gas line because the fuel supply is continuous — there is no tank to refill. Propane is ideal for rural properties where natural gas is not available; a dedicated tank is installed on your property and refilled periodically. Diesel generators are less common for residential use but offer excellent fuel efficiency for larger systems. Many modern generators are dual-fuel, meaning they can run on either natural gas or propane, giving you maximum flexibility. Your installer will help you choose the right fuel type based on your home's existing infrastructure and your location.
Next Steps
Once you know your recommended generator size, the next step is getting an accurate installed price from a licensed local installer. Generator costs vary by region, fuel type, and installation complexity. Enter your ZIP code above to see real pricing for your area and connect with top-rated installers — it is free, fast, and comes with zero obligation.