What Size Portable Generator Do I Need?

A portable generator is useful in many emergency situations. Whether you’re in a hurricane or tornado-prone area, or you simply need to ensure that you have backup power in case a serious power surge or outage affects you and your family, a portable generator can give you that peace of mind.

With a portable generator, you can keep your home’s most essential systems running, even if the main power grid is knocked out. But when it comes to shopping for a portable generator, you may be a bit confused.

Generators are complex. What’s the difference between running watts and surge watts? Does amperage matter? How many watts do you need to ensure you can keep your critical systems running?

In this article, we’ll provide you with a comprehensive guide that will allow you to choose a portable generator that’s right for you and your family. Read on, and get all of the information that you need about portable generators.

The Answer Is… “It Depends!”

Sorry, but this is the short answer! Obviously, we’ll tell you how to pick out an appropriately-sized generator in the next few sections, but the most simple answer to the question “What size portable generator do I need” is “It depends!”

It depends on a variety of factors, such as:

  • How many household appliances you need to power – If you are only interested in running some basic appliances like a few lights and your fridge or refrigerator, you will be able to get a smaller portable generator. However, if you need to power other, more power-hungry systems like heaters or air conditioners, you’ll need a larger model.
  • How long you’ll need to use your generator for – The length of time your generator will run depends on its power, fuel consumption, tank size, and a number of other factors.
  • The maximum wattage of all of your devices – You’ll need to select a generator that can handle the maximum running watts and surge watts of your household devices. We’ll explain this in-depth in the next section.

There are other factors, too – such as how many outlets you need, and other such issues. But, for now, let’s look at the biggest factor – the wattage you should choose for your generator.

Understanding Running Watts Vs. Surge Watts

To understand the size of generator that you’ll need, you must first understand the concept of running watts and surge watts.

Running watts is a measurement of how many watts an appliance takes up when it’s running. A 100w light bulb will consume (you guessed it) 100 watts for as long as it is powered by your generator. You will need to choose a portable generator that has a high enough wattage rating to continuously power all of the devices you intend to use in an emergency situation.

However, running wattage is only part of the puzzle. Surge watts must also be taken into account.

Some devices require a high initial “surge” of energy to turn on their motor, or to cycle on. This is called surge watts. Surge watts can be much higher than the running watts required for an appliance to keep running after they’ve been turned on.

Not sure what we mean? Here’s a table with a few common devices, to show you what we mean about the difference between running watts and surge watts.

Device type

Running watts

Surge watts (starting watts)

Refrigerator with freezer



Water heater (40 gallon)



Electric stove burner element



12,000 BTU window air conditioner



Garage door opener



35w light bulb






As you can see, some devices – mostly, devices like heating elements, light bulbs, and other “resistive” devices do not require surge watts, because they do not have motors that must be started with an electrical surge.

On most generators, you will see a rating for both surge watts and running watts. Typically, running watts are rated at about 90% of the surge watt capacity of a generator.

In other words, you can expect an 800w generator to supply about 720 watts of running wattage – and 800 watts of surge wattage.

If you continuously run a portable generator above its rated wattage, you risk losing power to your devices, and damaging the generator. You can’t expect consistent performance from a generator if its running or surge wattage does not meet your needs.

How To Figure Out The Size Of Portable Generator You Need – 5 Basic Steps

Okay. now that you know the difference between running watts and starting (surge) watts, it’s time to discuss the size of portable generator that you need.

It may seem really hard to pick the right generator – but it’s actually quite simple. We’ll show you how to do it in a simple, 5-step process.

  1. Select all of the items you wish to power at the same time – Let’s say that, for example, you want to be able to run one burner on your stove, your refrigerator/freezer, and a window air conditioning unit. Being able to run these appliances will ensure your safety and comfort when the power goes out.
  1. Next, list the running watts and surge watts of each item – One burner on your stove requires 2500 running watts, and 0 surge watts. Your refrigerator will need 800 running watts and about 1200 surge watts. The air conditioner needs 1200 running watts and 1800 surge watts.
  1. List the total number of running watts for the items you wish to power – In this example, our number would be 4500.
  1. Choose the item with the HIGHEST starting watt requirement – The air conditioner requires 1800 additional watts to start, so this is the item with the highest surge watt requirement.
  1. Add the item with the highest watt requirement to the number of total running watts – We would now add the 1800 watt air conditioner to the number of running watts we need, which is 4500. This means our total wattage requirement is 6300.This means that you need to choose a portable generator that has a surge watt rating of at least 6300 – that’s going to be the right size for you!

You may be wondering why we simply take the item with the highest surge wattage requirement and add it to the running watts – rather than adding all of the surge wattage requirements together.

This is because surge wattage is only required for a few seconds. Using a refrigerator as an example, 1200 extra watts are required to provide the 2000 total watts needed to get the motor to cycle on. However, after it begins to run, it will start to use less power, until it uses only about 800 watts.

Then, the “extra” power that’s freed during this process can be used to provide surge watts to another device, such as an air conditioner.

Therefore, there is no need to add together the maximum surge wattage when choosing a generator, because you’ll never be turning all of these items on at once, and they only need that “surge” of power for a few seconds.

Tips For Choosing A Generator That’s Right For Your Needs And Your Budget

Okay, now you probably have a good idea of how much power you’ll need in order to run all of your devices.

  • How many devices do you need to power? As a rule, we recommend only using your generator to power things that you’ll need in an emergency, such as your stove, refrigerator, or heating/air conditioning systems, if you live in an area with hot summers and cold winters.While it may be tempting to get a large generator that can power your entire home, this is very expensive, and you will likely pay a lot in fuel costs.However, if you live in an area where rolling blackouts are common and to be expected, it may be worth it. In contrast, if you rarely experience blackouts, you may want to get a smaller generator.
  • How do you intend to use your generator? You can use a generator for many things. Do you want a generator that’s portable enough to use in emergencies, and also for camping trips, or home improvement/construction in areas away from power sources? If so, a smaller and more portable generator is a good investment.In contrast, if you plan on hooking a generator directly into your home’s power systems, you will want a larger and more robust generator.
  • Do you need to run all of your devices continuously? If you don’t run all of your devices continuously, you can get away with a smaller generator, which will save you money on fuel.

Having Too Much Power Is Always Better Than Having Too Little

Here’s a rule to live by when choosing a portable power generator – it’s always better to get a generator that provides more power than you need.

Generators are expensive and if you try to get a small generator just to save money, you may end up simply having to buy a new one if your generator turns out to have a low wattage capacity, and it’s unable to power all of the appliances you need to keep working in an emergency.

Follow our tips to calculate the amount of wattage that you need, and ensure that you have plenty of power for all of your devices in an emergency situation.

Other Factors To Consider When Choosing A Generator

The wattage of your generator is only part of the puzzle when it comes to choosing a generator. Here are some other factors you’ll need to consider when you pick out a generator.

  • Number of outlets – More outlets is always a good thing. Most generators come with a number of standard wall outlets, and you can always use power strips to increase the number of total outlets available to you.You may also want to choose a generator that has a 30-amp 3-prong LV-30 connector, if you have an RV or another vehicle like a trailer, which you also want to power with your generator.
  • Run time – When you’re looking at generators, a common metric you’ll see is “run time at half-load”. This is a measurement of how long a generator can run on a single tank of fuel at half of its rated capacity.For example, a 5000 watt generator that has a 12.5 hour run time at half-load will provide 2500 watts for 12.5 hours.As a rule, you want to choose a generator that offers at least 10 hours of running time at a half-load. This means you’ll be able to sleep through the night without worrying about refueling – which is a huge benefit.
  • Portability – If you’re getting a portable generator, you’ll want it to be easy to move out of storage. Look for features such as locking and folding handles, and durable, large wheels that will help you move the heavy generator into place.
  • Cord set – Some generators come with free heavy-duty generator cord sets, which can “split” the power from the generator into multiple household outlets, eliminating the need for you to purchase your own extension cords.
  • Fuel/power type – There are a number of different types of generators available, including diesel, propane, gasoline, natural gas, and even solar generators.They all have their advantages and disadvantages. However, gasoline generators tend to be the least expensive and the best for emergencies, because fuel is easy to come by.

Follow This Guide – Choose The Right Size Portable Generator!

Hopefully, now you understand a little bit more about how generators work, and you’ll be able to find the generator that’s right for your particular needs! So start shopping now, and make sure that you’re safe and comfortable the next time your power goes out!

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