What Size Standby Generator Does My Home Need?

Generator size refers to how much electrical power a unit can supply at once, rated in kilowatts (kW). A standby generator has a maximum output, and the loads you connect to it draw against that capacity in real time. Sizing is the work of matching that output to what you actually want running during an outage.

Watt (W)

A unit of electrical power. Small devices are measured in watts.

Kilowatt (kW)

1,000 watts. Standby generators are rated in kilowatts — a 22 kW unit can supply up to 22,000 watts.

Every device has a running load — the steady power it draws while operating. But motors draw a much larger surge the instant they start. That starting load can be several times the running load and only lasts a moment, yet the generator has to be able to supply it.

The key sizing question isn't how much everything in your home draws — it's how much runs at the same time. A furnace, well pump, refrigerator and some lights running together set a very different requirement than a whole house running at full capacity.

This is why two homes of identical size can need very different generators. The loads, and how they overlap, decide the answer.

• Essential-load backup: heat, water, refrigeration and key circuits. A focused, smaller system.
• Expanded backup: the essentials plus added comfort and convenience circuits.
• Whole-home backup: the system carries most or all of the home's load, often using load management to handle large appliances.

None of these is automatically 'better.' The right level depends on what you want available and how you want the system to behave during a long outage.

Certain equipment has an outsized effect on sizing because of high running or starting demand:

• Well pumps — high starting surge; the source of all household water.
• Furnaces and heat controls — critical in a Northern Wisconsin winter.
• Central air conditioning — significant starting load in summer.
• Electric range and oven — large loads when electric rather than gas.
• Electric dryer and electric water heater — heavy continuous draws.
• Shop equipment and outbuildings — motors and tools add up quickly.
• EV charging — a substantial, sometimes continuous, added load.

Online charts that map square footage to a generator size assume an 'average' home. Real homes aren't average. Fuel type, whether heat is gas or electric, the presence of a well, air conditioning and shop loads all move the requirement up or down. A chart can produce a number that's confidently wrong for your property.

A practical first step is deciding what you actually want running. The tool below isn't a kilowatt calculator or a quote — it helps you build the load priority list that a proper assessment starts from.

A load-based assessment looks at your actual equipment, how it operates together, and how you want the system to behave during an outage. That's the difference between a generator that comfortably carries what matters and one that struggles — or one you paid for capacity you'll never use.