7 Tips to Choose the Perfect BTU for Your Home

Perfect BTU

Getting an air conditioner with optimal BTU (British thermal units) will help you cool your rooms more efficiently and save you loads of money.

That’s because improperly sized air conditions waste energy (because of the inefficiency) resulting in astronomical utility bills.

Tips to Choose Perfect BTU for A Home

Here are some practical tips to help you choose the perfect BTU rated air conditioner for your home:

Tip 1: Measure The Room

Start by measuring the room(s) to be cooled. To calculate the area, simply multiply the width times the length.

For instance, if my room is 15 feet wide by 18 feet long the area would be 15×18=270 square feet.

Tip 2: Calculate the BTUs

For starters, BTUs needed depends on the room size. Now, you can use the multiple online BTU calculators or read from our chart.

Before showing you the chart, here is how we calculate..

You will take the area (found earlier) then multiply it by 20 BTUs (20 is the standard required BTUs to cool one square foot).

So, this is how it would be: Area X 20 BTUs.

From my example:

The correct BTUs rating would be: 270×20= 5400 BTUs.

This means I would need an air conditioner with a minimum 5400 BTU rating (quite small).  

A quick question: Do such small air cons work?

Yes, they do. However, it has to be on for many hours which translate to higher electricity bills.

Here is the guiding table…

Square footageBTU rating/hour
300 – 3508,000
350 – 4009,000
400 – 45010,000

Whichever way, the BTUs indicated on the aircons unit should give you an idea on the ability of the models under consideration.

Here is the interesting bit:

BTU ratings are pure estimates and assume, among other things 10ft ceilings, sufficient insulation, and even windows.

Factors like excessive sun and random harsh climate will affect the accuracy. So, how do you get it right?

Tip 3: Reduce The BTU Capacity By 10%

Now, we said the whole thing is based on assumptions and you will need to make modifications based on your unique conditions.

First, is your room heavily shaded? If the answer is yes, take 10% off the figure in the table.

So in my case, I would pick 90% of 5400= 4860 BTUs for my cooler.

Tip 4: Increase The BTU Capacity By 10%

If your room isn’t shady but is instead always warm and bright, you’ll need more cooling.

So, you will crank it up by 10%.

In my example, this would now be 110% of 5400= 5940 BTUs…

Tip 5: For shared Rooms, Top it Up Further!

If we’re talking about shared facilities such as hotel rooms, each person needs a special treat so you go up again.

Actually, this time, you’ll add each additional person a whole 600 BTUs.

This means if my partner joins me in my sunny room, my aircon would be 5940 (Usual rating)+600=  6540 BTUs and if she carries a friend, it would be 5940+600+600=7140 BTUs.

And if it was in my shadowy room, my new aircon would be 4860+600= 5460 BTUs.

Tip 6: Add 4,000 BTUs!

Where you will install the unit also matters as far as calculating the BTU is concerned.

For example, if you will be mounting it in the kitchen where things usually get boiling hot, you need not less than 4000 BTUs on top.

So, if my room was sunny and a kitchen, I would be buying a 9,400 BTUs rated cooler (5400+4000).

Tip 7: Combine Rooms!

If you’re cooling two adjacent rooms and which are not separated by doors, you’ll need to add together the rooms when calculating the area since the conditioner will be cooling both spaces.


Getting the BTU rating correct is your most important step when buying an air conditioner. Simply calculate the area then follow the chart. And finally, make the necessary modifications.

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