How to Calculate the Running Cost of a Portable Air Conditioner

The summer months can get hot no matter what part of the world you live in. Even in colder climates, the heat can become unbearable and the humidity can be even worse. Fortunately for everyone out there, someone invented air conditioning!

What Does an Air Conditioner Cost to Run?

Air conditioners are wonderful inventions of modern living. They are a godsend for people living in hot climates but how much does it cost to run these units? I’ll take you step-by-step through the process of calculating this figure, and by the end of this article you should be able to understand the impact it’ll have on your bills.

Let’s start off by defining some common terms and language used in the air conditioning world.

What is a BTU?

The first step is to understand the technical terms involved. If you don’t understand the terms being used and the ones listed on your electricity bill, then you don’t have a chance when it comes to trying to figure out the cost. The British Thermal Unit (or BTU) is a term that you’ve probably heard but probably don’t fully understand. The BTU is the unit used in air conditioning to quantify the cooling power of the air conditioner.

In simple terms, one BTU is the exact amount of energy that is required for that air conditioner to cool one pound of water by one degree Fahrenheit. Sounds technical, and it is I suppose, but really it’s all about the power of your unit. Fortunately, you don’t have to calculate the BTU since the number is already listed on most units. If it’s not, you might need to enter your model number and manufacturer into Google to find out what it is.

Convert Tons to BTU

Some air conditioners state their cooling power in tons. One ton is equal to 12,000 BTUs of cooling power. So you can either figure out how powerful your air conditioner unit is by checking the BTU or the ton value and then do the conversion. If you have a 24,000 BTU system then it would equal two tons. Some bigger commercial systems measure in at 3 tons, which would be 36,000 BTUs. If yours was a smaller portable unit checking in at 6,000 BTUs it would be a half ton unit.

Most smaller portable air conditioning units are powered around the 8,000 to 14,000 BTU range. The lower end of the spectrum, 8,000 BTU, is enough for smaller single rooms. Those rated as 14,000 can cover large rooms and even small apartments. The big advantage of portable units is that you’re able to conveniently move them from room to room wherever they’re needed. Some areas of your home may get much warmer than others, or if you don’t spend much time in a particular room there isn’t much need to cool it off.

What is an Ampere or Amp?

The next term to understand is the Amp, or Ampere. This is a unit of electric current measurement to show how many electrons have passed through a single point in a given unit of time. Simply put, it is a measure of exactly how much electricity is flowing at a given moment. For any point experiencing a current of electricity, if the number of charged particles passing through it, or the charge on the particles passing through it is increased, the amperes of current at that point will proportionately increase. Fortunately for this step-by-step process we won’t be dealing with certain fluctuations. An old physics teacher of mine compared an Amp to the flow of water down a river – the more water that passes a point in the river, the higher the amps would be at that point.

Quick Guide to Energy Terms and Definitions

Check out our guide to buying the best air conditioner for you

The next term to be familiar with is the Joule. The Joule is usually displayed with the symbol J and it is a derived unit of energy in the International System of Units. It is equal to the energy transferred (or work done) to an object when a force of one Newton (another technical term we can skip for now) acts on that object in the direction of its motion through the distance of one meter.

It is also the energy dissipated as heat when the electrical current of one Ampere passes through a resistance of one Ohm (we won’t discuss that term much here) for one second. For this step-by-step guide it really isn’t used other than for helping understand what a watt is.

A watt is a measure of power. It’s the amount of power required to do an amount of work. Work, in this case, would be the ability to provide enough power to the air con unit to allow it to function. A kilowatt is 1000 watts.

The Volt is another important term in electricity.
It is a measure of the electric potential between two points on a wire. So picture this: one Amp moves one Watt worth of electricity across two points, and that amount is the Volt.

KiloWatt Hour
A KWh is a measure of energy
. It’s a measure of the power required to run an appliance over a period of time. So if an air con unit was rated at 1KW and ran for one hour it would consume 1KWh of energy. Likewise, if a 500w appliance ran for 2 hours if would also consume 1KWh. This is the basis for how all your electricity usage is measured and how the electric company figures out your bill. 

Step-by-Step Example

For the sake of this example I will use a 12,000 BTU portable air conditioner. This size of air conditioning unit is perfect for mid-size rooms around 350-400 square feet and is a common model to find in stores and online.

The first thing is to figure out how many Amps it pulls. Let’s say the 12,000 BTU air conditioner pulls 7.5 Amps.

The Math Bit – Calculating the Cost

For the next step in the process, you will need to know the voltage of your outlet. Standard outlets have a power voltage of 240 volts so I will use that for reference. You multiply the Amps and the Volts to figure out your total Watts.

Amps x Volts = Watts
7.5 Amps x 240 Volts = 1,800 Watts

Now you will take that number of Watts and calculate the Kilowatt-Hours. Remember, 1,000 Watts is 1 Kilowatt.

1,800 Watts/1,000 = 1.8 Kilowatt
1.8 Kilowatt * 1 Hour = 1.8 Kilowatt Hour (kWh)

The next step in the process is to find the average price a Kilowatt-Hour costs in your region. It can vary greatly from region to region and will also depend on the deal you have with your supplier. It should be clearly shown on your bill. For the purposes of this article, I will use 12.43 cents which is the average unit cost per KWh across the US.

So now that we have that number we can calculate the cost to run the unit:

1.8 Kilowatt-Hours x 12.43 = 22.374 or about 22.4 cents per hour

If you were to run that air conditioning unit for 6 hours a day you would simply multiply 22.4 cents by 6 hours

22.4 cents x 6 hours = 134 cents or $1.34 per day cost to run the unit.

If you were to run that unit 6 hours per day for every day of a 30 day month, the calculation would look like this:

$1.34 x 30 days in the month = $40.27 for the single portable air con unit.

It’s important to remember that many of these portable air conditioning units vary in energy ratings, sizes and power. It’s also important to make sure the unit is kept clean, particularly over the winter time so that any dust doesn’t clog up the filter as this causes your air conditioning unit to work harder and use more energy. This leads to higher bills and could also shorten the life of the unit.


For normal usage and average electricity cost it’s around $40 a month to run a 12,000 BTU air conditioner.

This is of course an average figure and so will change depending on your own circumstances, but with the process above you can plug in your figures for how often you use the unit, the wattage of the unit and your price for KWh to get a good idea of what a new or additional unit is going to cost you.

I hope you have found this information useful. Please let me know if you have any feedback or comments in the comments box below.

If you are looking to buy a new air portable conditioner you can check out our comprehensive guide. It’s packed with all the information you need to help you select the perfect unit for your home.

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