What Size Portable Generator do I Need?

If you’ve made a decision to get a portable generator, you may be wondering just what size generator you need. This will largely depend upon what you will need the generator for. A lot of people purchase a portable generator and then wish they had thought about all of the factors first. Generators are expensive, however, and you do not want to spend your money on the wrong one.


You will need to understand the difference between starting, or surge watts and running watts. All devices need a particular amount of watts to continuously run and some need more watts to start up or cycle on. This is the reason why portable generators are rated for their surge and running watts. On most portable generators, running watts are usually ninety percent of surge watts. You shouldn’t expect a generator to continuously run above its rated running watts.

Devices which don’t need surge watts are resistive types. Generally, these are devices that produce heat like toasters, light bulbs and coffee makers. Appliances and devices that have an electric mother in them need an added requirement of watts to start them up. This can be as simple as turning on a switch like with a power drill or hair dryer. For a refrigerator, starting is very different and will repeatedly start and stop. Closely listen to your refrigerator, and you’ll periodically hear it cycle on as the compressor, fan or defrost cycle begins. These surge watts can occasionally be two or three times the number of watts the device needs to just run.

What Size Generator Do I Need?

You will need to consider the watt requirement when calculating what watts you will need. For example, a standard refrigerator/freezer will need 800 watts to run continuously. When the compressor kicks in, however, it will need an additional 1200 surge watts. So a total of 2000 watts will be needed for ongoing power for your refrigerator/freezer.

Once it is settled into running, the watt requirement is 800, the 1200 watts that are left can be used for powering something else. With a low to mid watt generator that can have up to 3500 running watts, you can choose to run your refrigerator a majority of the time and then unplug it and switch the power for other needs, relying on the refrigerator to stay cold while the door is shut.

So, consider what you need your generator for:

  • Hooking into your home’s power to use as a standby
  • Emergency power when the power goes out
  • Using it on the job in locations which are remote and there are no electrical outlets
  • Using it now and then around your home
  • Tailgating, camping, RV use
  • All of these

Then ask yourself when you use the portable generator, what will you need to supply power to and how many devices need power at the same time? A good rule of thumb is to add up the running watts for a majority of the devices you need. Then add the highest surge watt need for any of these devices. You will then have the minimum watt requirement which you will need for the generator.