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Running Watts vs Starting Watts: What You Should Know

Running Watts vs Starting Watts
Written by Jamie Masterson

Running watts are the indication of power required to keep an appliance running whereas starting watts refers to the highest number of wattages required to start the appliance. These measurements are crucial for selecting the perfect backup generator for you.


A generator should be able to support both your total running wattage and the highest starting wattage. Let’s dig deeper and see how they differentiate.

What Are Watts?

Watts can be described as the unit to measure electrical power. It is measured by multiplying the voltage and the current of any electrical device. For those who aren’t familiar with the concept of power, it is the amount of work your machine can perform.

What are watts

Almost all electric devices/machines come with a power rating or wattage that showcases how much power they need to consume in order to function properly.

Running watts

Not every machine will require the same energy to work, but they still need a basic amount of energy flowing through them to keep them running. The energy your machine will require just to stay running over a set amount of time will be noted as the running watts of your machine.

In the case of a generator, this will express the amount of wattage your generator will be able to provide while it’s running. Most generators are equipped with circuit breakers that’ll trigger once the load is equal to or greater than the running watts your machine can handle.

your machine can handle.

Starting watts

Most large and heavy-duty electrical equipment needs a sudden surge of power to start working. This power can be 2-5 times bigger than its normal running watts. This sudden spike in energy requirement is known as the starting watts, surge watts, or peak watts.

The energy isn’t required continuously though. The machine will require the starting watts just for a couple of moments. Once the engine starts running at full capacity, the energy requirement will fall down to its original running watts.

Running Watts vs Starting Watts: How Do They Differ?

The primary difference between the running watts vs starting watts is the amount of energy needed and the time the energy is needed for. A generator can typically supply both these wattages and help your appliances run smoothly.

Appliances need around 2-5 times more energy than their usual state when they start working. The surge power AKA the starting watts is used to generate that initial momentum that will start the device.

What Is the Difference Between Starting and Running Watts

Once the sudden surge of power is over, the demand for energy drops and the running watts kick in. The device will continue to work at this minimum power level until it needs to start again. Your generator can easily supply this load over a long time.

Let’s hit the basics!

It’s time to dig a bit deeper. I’m confident that you probably learned about power, work, and energy in your high school physics class. For those who aren’t familiar, It takes more effort to move a heavier object and to move the same object further away, right?

The amount of effort won’t vary whether you are a man or a machine. The more you push a heavy object, or the same object to a location further away, the more effort it’ll take from you. This concept can be summarized in the equation below.

W = F * d

Where W = Work done (Joules), F = Force (Newtons), and d = Distance (meters)

W = F * d

However, we need another thing to calculate the power, and that is time. If the time is shorter, you’ll need to put more effort into moving the object and the opposite happens when you have a lot of time.

The measurement of work done over time is expressed through the term “Power” and is measured in watts. The more power you have, the more work can be done in a set amount of time.

So, the previous formula can also be expressed like this:

P = W / t

Where P = Power (Watts), W = Work done (Joules), t = Time taken to do the work (seconds)

P = W / t

Now, in comparison to the power generated from human strength, the electric power is a bit different. You’ll get the wattage (power) by multiplying the current (amps) and voltage (volts) passing through the machine. As a result, the above-mentioned formula becomes like this:

P = I * V

Where P = Electrical Power (Watts), I = Current (Amps), V = Voltage (Volts)

P = I * V

This is the most basic form of electrical power. In real-life applications, there are a lot more factors that will determine the wattage of your machine.

How to Size Your Load?

In order to properly size your load, you need to figure out and list all the appliances that you want to run on your generator. This will determine what size generator you’ll be needing.

Here is the chart of some common household items that can give you a rough idea:

Appliance Approximate Starting Watts Approximate Running Watts
Washing Machine 1600 800
Electric Clothes Dryer 6750 5400
Refrigerator 2200 700
Microwave Oven (1000 watts) 1500 1500
Television (16” Flat Screen) 190 190
Dishwasher (Cool Dry) 540 216
Electric cooktop 1200 1200
Garage Door Opener 1420 720
Sump Pump (1/2 Horsepower) 2150 1050
RV Air Conditioner (15000 BTU) 3300 2000
Blender 850 400
Hair Dryer (1600 watts) 1900 1800
Fan (portable) 120 40
Hand Drill (1/2 in.) 900 600
Automatic Washer 1200 1200

Once you make a list of all the appliances you need to run, add all the running watts to get the total running wattage. This is the lowest amount of wattage you’ll need from your generator continuously.

How to size your load

For the starting wattage, find the largest starting wattage in the list. This represents the highest amount of watts you’ll need from your generator. If you want to figure out the total wattage required during a surge.

The formula looks like this:

Total wattage requirement = Total running watts + Maximum starting watts. 

Using this formula, finding out the total wattage requirement for your generator will become much easier.

How To Choose the Correct Wattage

The only way to select the correct wattage for your backup generator is to go through the specifications the manufacturer provides. The specifications will include running watts and peak watts.

You need to make sure that your total running watts is within the generator running watt rating and the estimated surge watts stay comfortably within its peak wattage. Additionally, some outlets of the generator may have specific limitations on how much current it can handle.

How to choose the correct wattage

That’s why going through all the specs is really important when buying a generator. A general rule of thumb is to multiply your estimated surge wattage by 1.25 and select a generator that has a higher peak rating than the number you came up with.

This will make sure that your loads won’t surpass 80% of the generator’s capability.

What Happens When the Generator Overloads?

In times of overloading, the load draws more current than the circuit can supply safely. However, the voltage is usually determined by the power source, the load (with high wattage) will try to get more power by drawing more current.

The generator will resist the process by creating heat. The heat will increase with time until the machine burns out or worse, catches fire.

What Happens When the Generator Overloads

Some generators, however, can drop the voltage in time of overload. That isn’t good either. Alongside generating heat, this can cause permanent damage not only to the generator but also to the appliances connected with it.

In the worst-case scenario, you’ll end up with some broken appliances in the middle of a fire hazard.


Q. How to calculate the wattage of an appliance?

For the running wattage, you’ll need to multiply the amperage with the voltage. If any appliance needs 10A (Ampere) and 110V (Volts) to run, the running wattage will be = 10 * 110 = 1100W.

You can find the starting wattage by a Wattmeter. Usually, they are 2-5 times the running wattage.

Q. How much starting Watt does a refrigerator need?

That depends mostly on the size of the refrigerator, the production year, the brand, and the model. Usually, most modern refrigerators require a starting wattage somewhere between 500-2000W.

Q. How much running watts do I need for a portable generator?

The total running wattage should be greater than the combination of the highest starting power your appliances will need and the total sum of all the running wattage from all the appliances you want to power with the generator.

The formula is:

Total wattage requirement = Total running watts + Maximum starting watts. 

Q. How many watts does the average house use?

An average US home uses 900 kWh per month, which becomes 30 kWh per day or 1.25 kWh per hour. That means an average home in the US will require 1250W of wattage each hour.

About the author

Jamie Masterson

With decade-long experience as a generator technician, Jamie has worked with USA’s top generator manufacturers and suppliers as an independent contractor.

The long years of service to the industry has taught Jamie the ins and outs of troubleshooting, repairing, and maintaining all kinds of generators in home, industrial and outdoor settings.

Jamie thinks this platform is a great opportunity to share his tips and tricks with you so you can make the most of such power equipment for better living.

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