What Is CADR Rating? – Why Does This Rating Matter For Air Purifiers?

Although buying an air purifier might seem like a pretty straightforward task, it actually is not. You need to consider many things.

And if you have gone through any legit air purifier buying guide, you might have noticed that CADR rating is the topmost priority.

But what is CADR rating?

The CADR rating states how quickly the air purifier can remove the pollutants from the air in a room. Air purifiers with effective purification mechanisms will have a high CADR rating.

Now, why does moving the air faster makes such an impact in terms of air purifier?

Are the devices with a high CADR rating better than those with a relatively low rating? Read to find out!

Understanding CADR Rating – #1 Spec for Air Purifiers

CADR stands for Clean Air Delivery Rate. It is one of the most crucial metrics you must consider before buying an air purifier.

And as you know, this rating will let you know how effectively and quickly the air purifier can purify the air inside the rooms.

Likewise, this rating can give you an idea of the air purifier’s efficiency. Knowing that can help you make the right decision when making the purchase.

Let us provide a simple example to make your understanding a little more thoroughly.

Consider an air purifier “A”- with a maximum airflow rate of 300 CFM. “A” boasts a CADR rating of 200 CFM.

The first number states that the “A” can process 300 cubic feet per minute.

On the other hand, the second number says that “A” can effectively clean only 200 cubic feet per minute.

In other words, the first air purifying cycle will fail to clean the remaining processed 100 CFM.

Let’s give you another example. Suppose there is a “B” air purifier. It has a maximum airflow rate of 250 CFM. And it features a CADR rating of 220 CFM.

By comparison, “B” is a better air purifier even though its maximum airflow rate is 50 CFM lower than A.

Air Purifier CADR Ratings Scale

Depending on the size of the particle, the CADR scale can go up from 400 to 450.

The CADR rating has separate ratings for each pollutant to make things easier. Let’s go through those segments to give you a better idea regarding the scale.

Smoke CADR

This scale is for the smoke particles with a size between 0.9 microns and 1.0 microns.

The highest number on this scale is 450 CFM.


The dust CADR scale is for dust particles with a size between 0.5 microns and 3 microns. Its highest number is 450 CFM as well.

It is one of the first specifications that people look for before choosing the best air purifier.

Pollen CADR

This scale is for pollen particles that have a size between 5 microns and 11 microns.

The scale has the highest number of 400 CFM.

The CADR scales are basically there to offer you a relative performance indication.

And the scales are there to make it easier for you to compare the performance of one air purifier with another.

For example, the Dyson CADR rating is at 70. Although, this rating is not for all the models that Dyson has to offer.

There are a lot of things that come into the equation when it comes to putting an air purifier in the CADR scale.

Nonetheless, consider that one of the specific models has a 70 CADR rating.

On the other hand, the Levoit CADR rating is around 235. Again, that is for a specific air purifier that is from Levoit.

So, if you were to compare the Dyson air purifier with the Levoit air purifier, Levoit would take the lead in this case.

How Do You Calculate CADR for Air Purifiers?

The CADR rating is one of the crucial metrics for air purifiers. For that reason, the tests are standardized.

According to the directive of ANSI/AHAM AC-1-2006, all CADR tests must be performed in a test chamber that is 1008 cubic feet in size.

But why 1008 cubic feet?

Well, this test chamber will properly replicate a 12×12 room that has a 7 feet high ceiling.

That said, to perform the CADR test, the air purifier must be placed inside the chamber while running at full speed.

Afterward, manufacturers will take measurements of the number of specific pollutants. However, the measuring process does not end there.

After taking that number, the CADR rating is measured by considering how quickly the air purifier is moving all the pollutants inside the test chamber.

Finally, the air purifier ends up with a total CADR rating that has all three types of pollutants.

How to Estimate the CADR Rating?

Not all manufacturers go through the process of measuring the CADR rating of the air purifiers.

That is why you might face a little trouble while selecting the right air purifier for your home.

And there is a rule to estimate the CADR rating of air purifiers, the AHAM’s 2/3 rule.

So, for this rule, you will just need the maximum airflow CFM. You will find that in the spec sheet of all air purifiers.

According to the rule, the estimated CADR rating is 2/3 of the maximum airflow CFM rate.

For example, if the maximum airflow rate of a specific air purifier is 300 CFM. You can say that the estimated CADR rating of that air purifier is 200 CFM.

Now, do consider that this 2/3 rule might not give you the correct information. It is nothing but a process of estimating the CADR rating of the air purifiers.

Nonetheless, this 2/3 CADR rule can make it easier for you to choose the air purifiers that come with a CADR rating.

Any device that does not have a 2/3 CADR rating of the maximum airflow rate will not be that efficient in purifying the room.

So, if you happen to stumble upon something that has less than 2/3 CADR of maximum airflow rate, you should not put that into your consideration list.

Some Crucial Things that You Need to Know About CADR Rating

Although CADR rating is highly effective in choosing the perfect air purifier for your home, it is not the only thing you should consider.

Remember, the CADR rating only relies on the device’s efficiency when it is on the highest fan speed.

The rating does not give you any idea regarding the efficiency at lower fan speeds.

Also, the rating does not put the noise level into the equation, which is another important factor that you need to consider.

No matter how high the CADR rating is, a noisy air purifier will not be worth it.

Furthermore, the CADR rating will not tell you the ozone level the purifier creates.

It will not only state the efficiency of the UV-C light that might be present in the air purifier.

Finally, the CADR tells you the filter’s efficiency and how long it will last.

Frequently Asked Questions

1. What is a good CADR rate for an air purifier?

According to the 2/3 rule, any air purifier with CADR 2/3 of the maximum airflow rate is good. To put that into perspective, if you find an air purifier that has a CADR of 133 CFM with a 200 CFM maximum airflow rate, it has a good CADR rating. However, do consider the other important factors before making the purchase.

2. Is a higher CADR rating better?

The CADR rating states how quickly the air purifier can clear out the pollutants from the indoor air. And a high CADR rating would mean that the air purifier is faster at cleaning the contaminants. So, yes, the higher the CADR rating, the better.

3. How important is CADR in an air purifier?

The CADR rating is one of the crucial metrics you need to consider before purchasing. If you get an air purifier that does not have a CADR rating of 2/3 of the maximum airflow rate, it will not effectively clear out the pollutants that are in your home.

Read More: What Is A True HEPA Filter?

Read More: What Is HEPA Filter?

Final Words

So, what is CADR rating again? Well, in short, it specifies the ability of the air purifier.

It tells you how quickly the air purifier can get rid of the pollutants that are present in the air.

And when you are selecting an air purifier, the CADR rating is the first thing that you need to consider.

Last Updated on February 3, 2023

Richard Hicks

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