How Many BTU Should A Portable Air Conditioner Be?

Posted by: Mas Broto
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Portable AC BTU Room Size

Ever endured a summer day so scorching that even your thoughts start to sizzle? We’ve all been there, desperately wishing our living spaces could resemble the icy realms of the Arctic. That’s where a trusty portable air conditioner comes into the picture. But hold on! Before you rush to snag the nearest model, there’s a magic number to consider: the BTU rating.

Getting the right BTU size for a portable air conditioner is the secret potion for that gloriously cool summer indoors. This magic number isn’t a one-size-fits-all; it’s an individualized figure that spells the difference between a blissfully cool abode and a frustrating, sweaty ordeal. So, let’s unravel this cooling enigma together, shall we?

Decoding BTUs: What Are They?

In the simplest terms, BTUs, or British Thermal Units, measure the amount of heat an AC unit can remove from the air per hour. Too low, and your unit will struggle and strain all day without giving you the comfort you crave. Too high, and you’ll wrestle with clammy, excess humidity and an unhappily hefty electricity bill.

Essentially, a portable air conditioner’s BTU rating describes its power and cooling capacity and the higher the BTU value, the stronger the system.

Cooling capacities usually range from 5,000 BTUs to as high as 32,000 BTUs, and the size you need will depend on the area being cooled. If you choose a model with the wrong BTU value, your cooling efficiency can be affected.

A portable air conditioner with a higher BTU rating than the corresponding room size will cycle off too quickly, and the air conditioner will not properly remove the humidity from the air. On the other hand, if a mobile air conditioner has a lower BTU rating than the required room size, the unit will not adequately cool the room.

What Size Portable Air Conditioner Do I Need

Purchasing an air conditioner with the wrong BTU value for the space you’re cooling will result in problems with cooling efficiency, as an air conditioner that’s too powerful will cycle off too quickly and not properly dehumidify the room, and similarly, a unit with too low a BTU rating will not be adequately cool.

Follow the steps below to calculate your room’s square footage and find out the portable AC BTUs you need to properly cool your area from the preceding chart:

  1. Measure your room dimensions by multiplying the length by width. 
  2. Verify the size of your window opening. 
  3. Check the plug type and electrical requirements of your room. 
  4. Find the recommended BTU measurements from the chart below. 

To accurately find out how many BTUs your room needs, perform one of these two equations. Find the square footage of the room and multiply this number by 35 to get a general ballpark figure. Or, find the square footage of the room and find this number range in the following chart:

Room SizeRecommended BTUs
150 square feetup to 5,400 BTUs
200 square feet6,000 BTUs
340 square feet8,000 BTUs
400 square feet9,000 BTUs
450 square feet10,000 BTUs
550 square feet12,000 BTUs
750 square feet14,500 BTUs
850 square feet16,000 BTUs
1,000 square feet18,000 BTUs
1,400 square feet24,000 BTUs
1,520 square feet28,500 BTUs
1,600 square feet32,000 BTUs

For example, if your room measures 18 feet by 25 feet, your portable ac BTU calculations would look like this:

  • 18′ x 25′ = 450 square feet 
  • 450 square feet = portable air conditioner with 10,000 BTUs 

Alternatively, to get a quick ballpark figure of the BTUs, you will need for your room, multiply the square footage of the room by 35 to get a very rough estimate.

Additional Factors Influencing Your Portable AC’s Required BTU Capacity

Please note that the figures in the chart above are estimates based on average room conditions in a moderate climate; therefore, pay attention to the following exceptions if they apply to your room or home:

  • For sunny areas or second story and higher homes, add BTUs by 10%
  • For shaded areas, reduce the BTUs by 10%
  • For each additional person over two persons in a room, add 600 BTUs
  • For kitchen cooling, add 4,000 BTUs

Let’s dive into the specifics that can adjust this number, ensuring your new portable AC is neither overexerting itself nor underperforming.

Insulation Quality

Think of insulation as your home’s protective barrier against temperature extremes. Poor insulation is like wearing a sieve in a rainstorm; you’re still going to get wet! Similarly, with high temperatures outside, a poorly insulated space will take longer to cool down. The coolness dissipates faster when the AC is off, forcing the unit to work harder to maintain comfortable temperatures. If your insulation isn’t up to par, you’ll need an AC with more BTUs to compensate for the loss.


Are you blessed with a space that’s more shaded than a treehouse? If your room avoids the sun’s relentless gaze and enjoys the comfort of shade, you’re in luck. Spaces that are heavily shaded don’t need as much cooling power, allowing you to subtract 10% from the standard BTU requirement. It’s a little perk from nature that can save you power and money!

Natural Light

Now, if you’re basking in an abundance of natural light, your cooling needs will shift in the opposite direction. A sunlit room can feel like a greenhouse, trapping heat and demanding more from your AC. In this case, it’s wise to increase the unit’s BTU rating by 10%. This boost accounts for the additional warmth from the sun, ensuring your space remains the oasis you want it to be.

These factors, often overlooked, play significant roles in the efficiency and effectiveness of your portable air conditioner. By considering the unique attributes of your space, you ensure that you’re not just bringing an appliance into your home. You’re installing an optimized solution crafted for your comfort, one that caters to the environmental intricacies of your cherished space.


Understanding the precise BTU requirements for your space doesn’t just spell immediate relief on blistering days. It’s your long-term pact with efficiency, cost savings, and environmental kindness. Whether you’re a nomad adjusting to new spaces or seeking a quick cool-down solution for certain areas in your home, making informed choices about your portable AC’s BTU rating is your ticket to a chill, happy haven.

Once you’ve found your BTU requirement, click here to visit our selection of portable air conditioners to find the perfect model for your needs. Need help calculating your portable air conditioner BTU room size? Drop your comment below, and we’re always here to help.

mas broto avatar

Mas Broto

Have been in the heating and air conditioning (HVAC) industry for over 20 years. He is person that will grow and thrive to learn more about the HVAC industry throughout his career. Mas Broto is also a blogger, who's dedicated to bringing you the best knowledge to get ahead in the game of life.

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