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How Big of a Generator Do I Need to Run My Whole House?

So, you’re tired of being left in the dark during an outage. You’re probably looking at your options for a whole-home generator so you’re not stuck without power anymore, right?

To determine what size generator you need to power your whole house:

  1. Figure out the starting wattage (i.e. “surge” wattage) of the appliances and fixtures you want to power.

  2. Find a generator powerful enough to exceed the combined wattage of everything that needs electricity.

We’ll walk you through the process in more detail below. Before we do that, let’s look at how generators are sized.


Need an electrician to calculate what size generator your home needs? Give us a call at (800) 226-2636 or schedule an appointment online.

You can also check out our generator service page to get an idea of what we offer.


How generators are sized

Generators are sized based on their electrical output, not their physical dimensions. They’re measured in watts (W) or kilowatts (kW), both of which are a measurement of electricity (1kW = 1,000W).

It’s important to get the right size generator.

Why, you ask? Well, if you get a generator that’s…

  • Too small, you’ll overload the generator, or force it to supply more power than it can handle. If this happens, the generator will either automatically turn off or overheat, which will fry not only the generator, but also your costly appliances.

  • Too large, you’ll overpay for both the unit and the cost to operate it.

That being said, let’s look at how you can calculate what size generator your home needs.

Calculate what size generator you need in 3 simple steps

To calculate what size generator you need to power your whole home, follow these 3 steps:

Step 1: List out every appliance you want to power.

Step 2: Determine the starting and running wattage of everything on your list. If you can’t find these numbers on the appliance label, you can use this wattage estimation guide as a reference.

Note: Starting wattage (also known as “surge wattage”) refers to the wattage an appliance needs at start-up. Starting wattage is normally 2–3 times higher than its “running” wattage, or how many watts an appliance needs to run constantly.

Step 3: Add the wattage together. Then, use this number to guide what size generator you need.

Keep in mind that a DIY wattage estimate is just that: an estimate. To be on the safe side, we recommend using a wattage calculator or, even better, having a professional electrician calculate the exact wattage you need to help you find the right size generator.

If you’re up for trying it yourself though, let’s look at a couple examples.

Power just the essentials

If you want to power just the “essentials”, your list might look something like this:

Appliance 1

In this case, you’d need at least a 25kW generator, since the starting wattage is 24,100W.

Power your whole home

If you want to power just about everything in your home, your list would probably look more like this one:

Washing Machine

In this situation, you’d probably want at least a 35kW whole-home generator.

Need a pro to help you find the right size generator?

We’ll send an electrician to your home to calculate the exact size generator you need.

Learn more about our services and generators we install on our generator service page.