Generator Wattage Calculator – Find Best Generator For You

July 1, 2020

Imagine that you just bought a generator. You connect it to whatever you are planning to power and realize that it is not doing what it’s supposed to. And we are pretty sure that it won’t take you a moment to understand that you have just wasted your time as well as bucks. So, how to avoid such an incident?

Well, this is where a generator wattage calculator comes into play! You can use a wattage calculator to determine how much power can a specific generator output. And once you learn how to use it, you will never face such a predicament in your life.

Now, using it can be a tad tricky! So, to make the process easier for you, we have come with this calculator.

Let’s begin? 

How to Use This Generator Calculator?

Step 1
Select the Purpose for Your Generator
Step 2
Select Appliances You Need to Power by The Generator
Step 3
Choose a Generator From Our Recommanded List

Step One


  • Home back up power
  • Primary home power


  • Construction/Contractor
  • Rental fleet
  • Farm/Agricultural


  • RV vehicle Camping
  • Tailgating Outdoor events

Basic Terms & Watt Calculation

Before you learn how to calculate the wattage required by your appliances, you need to first learn about running-watts and starting-watts. What’s the difference? 


Running watts are the continuous watts needed to keep tools and appliances running. Running watts in a generator suggests the amount of power a generator can supply continuously at any given time. 


Starting watts are the Additional Watts required for a brief moment (3-5 seconds or so) to start motor-driven appliances, tools, or products. In a generator, starting watts suggests the temporary boost of power a generator can supply when attempting to start a device with a motor. Appliances like air conditioners and welder have very high starting watts requirement compared to their running watt requirement. It also helps to know that there are different types of motors.

Induction Electric Motors

  • It requires more power to start.
  • For some appliances, they need up to 6times more starting power than their running power. 
  • Used in ACs, fridges, and water pumps.

Armature Electric Motors

  • It requires less to no starting power.
  • Used in hairdryers, vacuums, and other power tools.

How To Calculate Wattage

It’s vital to know how much starting power you will need from a generator and which appliances you will use that may or may not require starting power. All generators have running and starting watts limit, and the amount is included in the generator itself.

So, you must get a generator that can provide sufficient power to allow different appliances to start-up while other devices are already running.

What if you can’t figure out the running watts or starting watts requirement of specific equipment that you want to power using your generator, especially if it’s not stated or shown on the machine?

Use this equation,

Watts= Volts x Amps.
Watts (P = V x I.) 

When you turn on a motor, it gets a momentary rush of electricity, and this makes the motor active. For a brief period, the motor acquires a little resistance. As a result, a high current flow occurs, and the magnetic fields around it form by pulling and pushing each other, forcing the motor to rotate. 

The rush of currents also called surge, tapers down quickly as the motor reaches it’s required RPM. A motor that needs 6 Amps at full load should require around 18 Amps to start Starting Watts).

If it has 120V, you multiply Volts X Amps and get 6 Amps X 120 Volts =720 Watts.

This is what you would call running watts requirement for that specific motor.

Now, you do the same for starting watts (using 18Amps instead of 6Amps), and you will use the equation again. 

18A x 120V = 2160 Watts. 

This is the starting watts requirement for that same motor

Since that’s out of the way, we can now move onto calculating the maximum watt requirement of all the appliances together. Not all devices require additional watts, as we mentioned before.

How We Calculate the Required Generator Wattage?

Total Running Wattage – We calculate this by summing all the running wattage ratings of each device. It is ensured that we are only using Running Watts.

Minimum Starting Watts – This is the minimum surge power required from your generator to avail you to run your appliances without any risks. To calculate this, we add the surge rating of a device with the highest starting watt requirement following the Running Watts of the other peripherals. 

Maximum Starting watts requirement – We start by adding all the Starting Wattages of all the appliances that will be used with a generator After adding the sum together, we will have the Maximum Starting Watts. This is the recommended generator Starting Watt rating.

Why You Need to Opt for a Bigger Generator

Why should you go for a generator that is bigger than you need might be a question that is running around in your head! Well, there is always a reason for that. We are quite sure that you check out the reasons here, you will finally understand.

  • Reason One

It is always a smart idea to opt for something that is bigger than ending up with something smaller, in the case of power. If you end up with something that outputs lesser than the required amount, then you might not be able to operate all the devices that you want. 

On the other hand, buying something that is slightly bigger might be a tad costly. However, it does prevent you from needing to go through the entire screening process all over again. Plus, the chances of you not being able to operate all your appliances and devices diminishes if you go for a more robust generator.

  • Reason Two

Another reason for buying a generator that is not neck-to-neck with the required wattage is that you will significantly shorten the generator’s life. You see, having a generator that just fulfills the required wattage will continuously be running at full load, which is quite harmful to the device.

  • Reason Three

By the way, the noise produced by a bigger generator will be significantly less. As you have a bigger generator, it would need to work less to provide the required wattage, which means less work and less noise. Thus, using a more powerful generator might prove to be more pleasant. 

Portable Generator VS Whole House Standby Generator

Well, as the name suggests, portable generators are generators that are easy to move around. These are a remarkable option for outdoor activities such as backyard parties, camping, BBQ, etc. And these types of generators are quite handy and are not as much of a nuisance that generators are known to be! 

Though they can be used to output a serious amount of power, when compared to standby generators, they lack in the power department. A standby generator acts as backup power in case there is a blackout or power failure. They are known to out a heavy amount of wattage.

But standby generators can be quite heavy and difficult to move around. And when it comes to pricing, standby generators might be quite expensive. On the other hand, portable generators lack several features that a standby generator can provide the user.

In short, both the generators are excellent! And it depends entirely on the user’s preference. If you are planning to do some outdoor activities, then portable generators are a good option. However, if you want to keep a backup power system for your home, then a whole house standby generator is definitely the best option. 

Traditional Generators VS Inverter Generators

Generators were first discovered in the 18th century and have become a very important factor for the human race. However, over a few years, generators have changed quite a lot. So, in this section, we shall be pinning traditional generators against inverter generators.

One of the most obvious differences between the two is their outlook. But that is not all! These two have several other diversities, and one of the biggest differences is the current. Traditional generators are known to output an AC, which is.

On the other hand, inverter generators output a non-fluctuating 3-phase AC. The current outputted by the device has a much more stable sine wave! By the way, when it comes to efficiency and fuel consumption, inverter generators beat traditional generators in this race as well.

Inverters are also known to be noiseless, reduces pollutant emissions, provide parallel connection, and more.

In short, inverter generators are more modern and superior of the two. Traditional generators are not bad. However, the remarkable number of features and the vast number of perks that an inverter generator has to offer makes it a better option. So, in the fight between traditional and modern, the inverter generator wins!

Generator Brands We Include on Our List

Frequently Asked Questions

Here we have the most commonly asked queries regarding wattage calculation:

  • How to calculate wattage?

Well, calculating wattage is no rocket science. Wattage is equivalent to voltage times ampere. So, find the voltage and ampere of a device, and if you multiply the two, you will get the number of watts you need to operate it.

  • How to calculate what size of generator I need? 

To calculate the size of the generator, you need to make a list of the appliances or devices that you are connecting to the generator. After you have done that, add the required watts to operate each of the devices, and you shall the size of the generator you need.

If you want the optimum performance from your generator, then understand how to calculate the generator size is imperative. And after you are done with our article, we hope that you understand how to calculate wattage.