Generator Guide: How to Find the Right Size to Fit Your Needs

D.P. Taylor
Written by D.P. Taylor
Updated September 15, 2021
House lit up on snowy night
Aleksey Sergeychik -

You will need to install a whole-house generator to power appliances and devices in a home, but you only need a portable generator for a camping trip or small outdoor event

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We all take electricity for granted until we no longer have access to it. All of a sudden, the food in your fridge is going bad, you can’t charge your phone, and you have no Wi-Fi. 

Whether you’re dealing with a blackout or think a generator would come in handy while camping, you might consider getting one for situations like this. But what size do you need? It’s an important question, and this guide will help you calculate it with high accuracy.

How to Calculate the Size of Generator You’ll Need

Determining the size of the generator you need to purchase depends heavily on what the generator will do. If you just want one for camping, you won't need a very large generator. But if you want a whole-house generator for emergencies, obviously you need quite a bit of power.

You'll need to do your homework to avoid buying a generator that can't handle your energy needs, or spending too much on one that is way more powerful than you need. Follow the step-by-step process below to calculate the correct size as accurately as possible.

List the Energy Usage of All Devices and Appliances

The first step is to list all devices and appliances you want to keep powered, as well as their individual energy usage.

For example, if you want a generator that can keep the following appliances running during a power outage, you'll need a generator capable of producing at least 5,700 watts.

  • Refrigerator: 600 watts

  • Large window air conditioner: 1,400 watts

  • Large dehumidifier: 700 watts

  • Water heater: 3,000 watts

Determine Starting Watts

Now that you have the baseline wattage you'll need, it's time to find out if you need any more. Many appliances, such as air conditioners, require "starting watts'' when turned on, and then the energy usage declines to its "running watts” (or rated watts). As a result, you'll need to add any starting watts for your appliances to that total to ensure the generator can handle starting them up.

Most generators list “rated watts” and “starting watts,” with the latter always larger than the former. You need to know both figures for all your devices and appliances before you choose a generator.

Call your manufacturer if you are uncertain what the starting and running watts of your appliances are. Regardless, it’s always smart to choose a generator slightly bigger than what you think you need.

Choose the Right Type of Generator

Now that you know what wattage you need, you also need to choose the right type of generator. There are three to choose from: portable, inverter, and whole-house generators.

Whole-House Generator

In the above example, where you're trying to run home appliances, you'll want to go with the whole home generator, which is suited for backup of your home in case there's an outage. These are hardwired systems that can take over in case the grid goes down. Note: Run them outside as they produce carbon monoxide.

Inverter Generator

If you're looking for a cleaner, quieter generator that doesn't need to produce much power, an inverter generator might be the best choice. They’re more fuel-efficient, and might save you some money. They are often used in RVs due to their ability to convert AC power to DC power.

Portable Generator

A portable generator is the right choice if you just want something to provide power on a camping trip or a small event. They have limited power, but in these scenarios, you typically don't need as much. And their portability is a big benefit.

What Will Certain Wattage Levels Support?

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If you're wondering what a generator will support depending on its wattage levels, this guide might help.

2,000 Watts

A small recreational generator can power a large appliance like a refrigerator and a few smaller devices, such as laptops or amps.

4,000 Watts

At this level, you might be able to power two large appliances and some smaller devices, but it won't cover all of the essential electricity needs of your home in the event of a blackout.

8,000 Watts

A generator with this level of energy output can handle most of your essential appliances and devices, including a well pump or even your dishwasher. However, you'll still need to leave some appliances off the list.

20,000 Watts

This generator can power everything in your house as if you were still on the grid.

How Much Does It Cost to Install and Run a Generator?

If you're getting a new whole-house generator installed, you can expect to pay between $1,400 and $7,700. Of course, those costs vary greatly depending on the size of the generator. A small portable one may cost only a few hundred dollars, and have no installation costs.

The cost to run the generator varies depending on wattage and type. However, generally you can expect to pay $20 to $40 per day to run a whole-house generator. And since generally you're running it only for a few hours at a time, or a few days at most, you may only pay a couple hundred dollars per year in operating costs.

You should factor in occasional home generator repair costs as well, which average $260.

Ready to Get Your Own Generator? Consult With a Professional

A generator is a big decision, and it's important that you install one correctly if you're getting a whole-house generator. A professional can take a look at what appliances and devices you want to run and determine the correct size without you having to do the calculations yourself and potentially make a costly error.

Contact a home generator installer in your area for a consultation. They can provide recommendations and a price quote so you don't have to worry about the details.

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