What Size Portable Generator Do I Need?


The world runs on power—whether you’re running your HVAC system at home, adorning your RV with outdoor lights, or operating power tools on the job site, you need reliable access to electricity.

But, electrical power availability isn’t always a given. When your power goes out during a summer storm or when you need to charge electronics at a remote campsite, a portable generator can be a saving grace, keeping you connected wherever and whenever you need it.

But, shopping for a standby generator isn’t without its challenges. As you browse your options, you may ask, “What size portable generator do I need?” 

In this guide, we’re breaking down everything you need to know about portable generator sizing. In a market with nearly countless options, we’ll help you choose the perfect size by exploring the importance of portable generator size and wattage considerations, calculating your needs, and finding the sweet spot. 

Demystifying portable generator sizes can be challenging—our experts are here to help.

Why Does Generator Size Matter?

Before we jump into the importance of size, let’s break down how a generator works:

  1. A mixture of fuel (gasoline or liquid propane, for instance) and air combine in a combustion chamber.
  1. The fuel is ignited by a spark plug, creating a combustion reaction that forces the pistons to move down and the crankshaft to rotate.
  1. As the crankshaft turns, it spins the rotor inside an alternator, which generates an electrical current—power you can use.

Regardless of size, all fuel-powered generators perform two crucial conversions:

  1. Converting chemical energy (the energy stored in fuel’s chemical bonds) to mechanical energy (the energy produced when the pistons, crankshaft, and rotor move)
  1. Converting mechanical energy to electrical energy (via the alternator, which spins a rotor in an electromagnetic field to produce a charge)

So, all generators do the same thing, but they produce different amounts of power (wattage) based on size. Why? The larger the generator, the more fuel it can hold, and the larger the pistons are. With more fuel and larger pistons (which produce additional energy), a larger generator produces more power.  

Understanding Wattage

Wattage is the amount of electricity required to operate a device, tool, or electrical appliance. A device’s wattage is equal to the voltage (the “strength” of the charge, measured in volts) multiplied by the current (the charge’s flow rate, measured in amps). 

Generator size is generally measured in watts—the amount of electricity they can produce. But, there are two different elements to consider when calculating the wattage your portable generator will need to provide. 


The Wattage Calculation

To determine how many watts your ideal backup generator should produce, perform a simple calculation:

Total of all running wattages for all devices you wish to power + Highest starting wattage of the motor-powered devices you wish to power = Minimum required wattage.

Let’s explore both elements of this equation in more detail. 

Running Wattage

Running wattage is the continuous power required to operate a device that’s already running steadily. For instance, once your HVAC system starts, it will require running wattage to maintain cooling or heating functions after the initial start up.

A critical part of the wattage equation above is the total running wattage of all the devices you want to power at a given time. Let’s explore an example.

If the power goes out during a summer storm, you may want to run the following devices simultaneously:

  • Air conditioners
  • Electric water heaters
  • Refrigerators
  • Televisions
  • Lights
  • Cell phone chargers
  • Septic system sump pumps
  • Well water pumps
  • Computers
  • Electric cooktops
  • Microwave ovens

While it’s unlikely that all of these devices will be running simultaneously (if you live alone, you’re unlikely to be running your electric stove, taking a hot shower, and using the microwave all at the same time), you should choose a generator size that can hypothetically manage the simultaneous power demand of all of your chosen devices. 

Thus, you should calculate the total running wattage of all of the devices you imagine you’ll run on your generator at one time. 

Each device should include wattage information in the user manual. If you can’t find wattage information for a device, err on the side of caution and use a high wattage estimate. 

Starting or Surge Wattage

Electronic devices with motors or heating elements require extra energy for a few seconds when they start up—these are called starting watts, or surge watts.

When you calculate how many watts your generator must produce to meet your power needs, you must account for starting wattage for devices that rely on motors or heating elements, like:

  • Refrigerators
  • Dishwashers
  • HVAC equipment
  • Washing machines
  • Vacuum cleaners
  • Microwaves
  • Electric and ceiling fans
  • Blenders
  • Power tools, including:
    • Circular saws
    • Some sanders
    • Electric jackhammers
    • Electric weed eaters

It’s important to make a list of starting wattages for all motored devices you plan to power with your smaller generator. But, your equation only needs to account for the device with the highest starting wattage requirement. Why?

  • While you may be running numerous devices simultaneously, you’re unlikely to be starting them all simultaneously. 
  • Choosing the highest starting wattage covers your bases for all of your other devices’ starting power needs. 
  • Adding the highest starting wattage to the sum of all running wattages will ensure that your generator can start your devices one by one and sustain their running wattage requirements. 

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Common Wattages to Consider When Calculating Generator Size Needs

When you use the formula listed above, you ensure that your generator can sufficiently start and power all of the devices you wish to run. You can also use a portable generator size calculator.

Let’s explore some standard wattages in various use scenarios to help you determine which portable generator size is right for you.

Home Use

You might experience home power outages during hurricanes, winter storms, or routine utilities maintenance. Let’s explore a few average running and starting wattages you might encounter in a home power outage scenario:


Running Wattage

Starting Wattage

Central air conditioner






Ceiling fan



LED light bulb



36” TV



Hot water heater



Well pump



Electric cooktop



Total Running Wattage


Highest Starting Wattage



The devices and appliances in your home will each have unique wattage requirements—the figures above are just examples.

Assuming you want to run all of the above devices during a home power outage, you’ll need a generator that can produce at least 14,045 watts—11,045 + 3,000 = 14,045. 


Job Site Applications

If you’re looking for a right size generator that can power all of your equipment on the job site, carefully review your tools' wattage requirements compared to your power requirement. Some standard tools and estimated wattage requirements include:


Running Wattage

Starting Wattage

Air Compressor



Airless Paint Sprayer



Hand Drill



Miter Saw



Belt Sander



Circular Saw



Quartz Halogen Work Light



Reciprocating Saw



Total Running Wattage


Highest Starting Wattage



Depending on the size of your crew, your trade, and the type of project you’re working on, you may not be using all of these tools simultaneously. But, in a scenario where all of the above tools are running simultaneously, you’ll need a generator that can produce at least 12,560 watts—8,960 + 3,600 = 12,560.



For an RV trip, a weekend at the hunting camp, or an outdoor event, an RV generator for camping provides convenient power access. But, how large should your portable generator be for recreational use? Let’s examine another table of everyday devices and their estimated wattage requirements:



Running Wattage

Starting Wattage

AM/FM Radio



Cell Phone Battery Charger



RV Air Conditioner



Coffee Pot



Inflator Pump



Electric Blanket



Portable Heater






Total Running Wattage


Highest Starting Wattage



Depending on the scenario, it’s unlikely that you will run these devices simultaneously—you likely won’t need electric blankets, a coffee maker, or an inflator pump for an air mattress at an outdoor wedding, for instance. 

But, to estimate average recreational use, let’s sum the wattage needed to power all of the above devices simultaneously—2,935 + 1,500 = 4,435. So, you can probably meet your recreational needs with a portable generator that can produce around 4,000 watts


Size Considerations: Finding the Sweet Spot

Wondering, “what size of portable generator do I need?” Determining the appropriate generator size for your application can require estimating. Still if there are too many hypotheticals to consider, you might be tempted to oversize or undersize your generator to err on the side of caution or save money, respectively. But, this isn’t always the right call. 


Preventing Generator Overloading and Overheating

If you exceed your generator’s maximum wattage capacity, you may overload or overheat your generator, which could cause one or both of the following issues:

  • Damage to your generator
  • Damage to your devices or appliances

If you opt for an undersized generator and you want to avoid overloading or overheating, you can:

  • Reduce the number of devices you’re powering with the generator
  • Run high-wattage appliances (like A/C systems and hot water heaters) one at a time
  • Opt for gas-powered tools or devices on the job site instead of electric tools

While most standby generators have an automatic shutoff function as a safety precaution in the event of overloading, constantly stressing your generator with high energy demands can increase the risk of malfunctions. 


Bigger Isn’t Always Better

If it’s easy to overload an under-powered generator, why not just start with more wattage than you need? Here’s why a larger generator may not always be the answer: 

  • High up-front costs of large generators – Whole-home backup generators and high-wattage generators can be expensive to purchase, install, and maintain.
  • You may overestimate your use – While you might think you’ll need to run your A/C system, dishwasher, cooktop, TV, and hot water heater simultaneously during a summer storm, you may proceed more conservatively in reality.
  • Increased life cycle costs – Larger machines require a larger investment in maintenance and backup supplies (like fuel and lubricants). 
  • Limited space – While you might want the peace of mind that a massive house generator can provide, you may not have the space to store or operate a larger machine.

Instead of choosing the largest, most powerful generator on the market, select the right generator based on a realistic assessment of your needs, your available space, and your budget. Small generators are ideal if you have a limited budget and a smaller space.


DuroMax Can Help You Find the Right Size Portable Generator for You

Choosing the right portable generator size isn’t always easy, and with so many options on the market, selecting the perfect product can be a daunting task. Generators are a significant investment, and you should use all the resources available during your search.

At DuroMax, our experts are prepared to help you choose the right portable generators for the job, giving you access to power whenever and wherever you need it. Whether you’re mulling over your wattage needs or struggling to stay within your budget, our team has the experience and expertise you need to choose the perfect backup power solution.