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What Size Generator Do I Need to Power My House During an Outage?

Generator wattage

So you’re tired of getting left in the dark during these infamous Arizona summer outages and you’re ready to invest in a backup generator.

But you have no idea what size generator you need.

Luckily, you’re in the right place. We’ll go over everything you need to do to make sure your generator matches your power needs.

First though, let’s take a look at how generators are sized.

How generators are sized

Generators are sized in watts (W) or kilowatts (kW). Both watts and kilowatts are a measurement of electricity. (1 kilowatt=1000 watts)

So, a generator’s size has nothing to do with its physical measurements. It refers to how much electrical power it supplies.

But what happens if you get the wrong size generator?

A generator that doesn’t provide as much electricity as you need can cause a voltage drop and damage both your appliances and your generator (or it will stop supplying power altogether). But go too big and you’ll end up overpaying for the unit and the operational costs.

So let’s take a closer look at the steps you’ll need to follow to find the perfect size generator for your needs.

3 steps to calculate the exact size generator you need

Step 1: Make a list of all the appliances you need powered in the event of a power outage

Step 2: Determine the starting and running wattage of each appliance on the list.
We know you most likely aren’t familiar with these numbers off the top of your head, so here’s a comprehensive “wattage worksheet” that will be useful for this step.

Note: The “starting” wattage of an appliance refers to how much electricity it needs at start up. Starting wattage is typically 2 to 3 times the wattage it uses when it’s running continuously.

Step 3: Add up the total wattage needed and base the generator size you need on this number.

So the generator size you need really depends on the amount and type of appliances you want powered in the event of an outage.

Let’s look at an example…

Homeowner A and Homeowner B are both shopping for a backup generator and both have a 2,000 square foot home.

But their power needs are very different so they’ll need different sizes of generators.

Homeowner A: Just the essentials

Homeowner A chooses to power only “essential” appliances during a power outage.

So their list might look something like this:


Homeowner A might be interested in investing in a 11kW backup generator.

Homeowner B: Whole-home power

Homeowner B is looking to provide power for his entire house, not just essential appliances.

Their process will be the same, except homeowner B’s list will be longer because they want to power their entire home during an outage.

Their list may look something like this:


So homeowner B would be more interested in a 40kW whole-home generator.

Want to take a stab at measuring the wattage you need?

Keep in mind that DIY wattage measuring is always a rough estimate. Having a professional electrician inspect your home and calculate your electricity needs is your best answer.

If you’re up for the challenge, though, we recommend using a wattage calculator like this.

Ready for the next step?

Once you know the correct size generator for your electrical needs, take a look at our Home Backup Generator Buyer’s Guide for all your generator questions.

Need a professional to install your generator for you? We’re happy to help.

Just contact us today and we’ll set up your appointment pronto.

George Brazil’s licensed and trained electricians have been serving Phoenix-area homes since 1955. Contact us online for more information about any of our services.

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