What Does the CADR Rating Mean on an Air Purifier?

My first time buying an air purifier was very confusing.

To start, many of the various types on the market can be confusing.

On top of that, choosing between the options usually means looking at various measurements and specifications.

And one particular measurement that caught my eye was CADR.

‘CADR’ was mentioned on most of my top options, but I had no clue what it meant.

But when I went on the internet to figure it out, I had difficulty finding a straight answer.

So, I’ll explain what CADR is as straightforward as possible in this article.

I also explain how CADR is measured, the ideal CADR rating for air purifiers, and other necessary specifications to keep in mind.

Read on to learn more.

What Is CADR?

Before getting into technical definitions, let’s start with what CADR stands for.

CADR stands for “clean-air-delivery-rate” and is basically how well an air purifier cleans the indoor air in a testing chamber.

The CADR is arguably the most important measurement when buying an air purifier, as it clearly defines its effectiveness.

A high CADR rating shows that an air purifier can remove certain particles from the air effectively and quickly.

A low CADR shows that an air purifier isn’t that effective.

Manufacturers may test their air purifier’s CADR internally. However, they still need to verify the results with a third-party laboratory.

This is why learning the CADR of an air purifier can help you determine if it’s the right size for your space.

What Contaminant Levels Are Measured with CADR?

When manufacturers test an air purifier’s CADR, they measure its ability to filter out specific pollutants.

Air purifiers typically have three different CADRs, one for each pollutant.

There are smoke, dust, and pollen CADRs.

Measuring the CADR for specific particles is essential as pollen, smoke, and dust particles come in different sizes.

So, an air purifier may have a high pollen CADR to eliminate larger particles effectively.

But a low smoke CADR means it can’t handle smaller particles.

How Do You Measure CADR?

Manufacturers measure CADR through a standardized procedure to ensure consistency and reliability in the results.

To follow standard procedure, manufacturers must test their air purifiers in a 12 x 12-foot room with a 7-foot high ceiling.

Every CADR test will be conducted in a room with the same air volume to produce reliable results.

Before turning on the air purifier and placing it in the testing chamber, they need to measure the number of pollutants in it.

Then, with the air purifier at full speed, the manufacturers measure how quickly the air purifier removes the particles.

This test gives you the smoke, pollen, and dust CADR rating, which the testers use to calculate the air purifier’s overall CADR.

Manufacturers use this test to provide steadily reliable results that you can use to gauge an air purifier’s overall effectiveness.

What’s the Ideal CADR Rating for Air Purifiers?

While the general rule that a higher CADR is better is true, this isn’t the best way to look for air purifiers.

Searching for an air purifier with the highest CADR available will get you the largest air purifier, not the best one for your needs.

Some manufacturers don’t even put the CADR on their air purifiers, making things even harder.

That said, if the manufacturer does have the CADR posted, it’s essential to compare the rating to the size of your room.

Ideally, you want to get an air purifier with a CADR that’s at least ⅔ of the area of your room.

For example, if you have a room that’s 150 square feet, then a CADR of 100 would suffice for the room.

Sometimes, the manufacturer will place the maximum airflow of the air purifier.

This is expressed in cubic feet per minute, which shows how much air volume the purifier can handle every minute.

You can get the air purifier’s CADR from the CFM rating since the CFM is around ⅔ of the CADR.

So, if the air purifier only lists the CFM, it’s best to get an air purifier with a CFM that matches your room.

The previous example would mean a 150-square-foot room needs a 150 CFM air purifier.

Other Air Purifier Specs You Need to Know

I learned that the CADR was the most crucial metric when buying an air purifier.

However, this isn’t the only specification that you’ll come across.

You must consider all the specifications to find the best air purifier for your needs.

Here are some more air purifier specs that you might come across while shopping:


As mentioned earlier, this refers to cubic feet per minute. 

This shows how much airflow the machine can handle. 

And to get an air purifier that can handle your room, it needs to have the same CFM as the area of the room.


ACH means air changes per hour and refers to how many times the air purifier can replace the air volume in a room.

The ACH accounts for the air purifier’s CADR in relation to the room size.

For example, an air purifier that can provide 5 ACH in a 150-square-foot room replaces the air inside the room 5 times every hour.

Ideally, you would want an air purifier that provides at least 4 ACH for your room.

That way, you completely change the air inside every 15 minutes, meaning you won’t have any particles and pollutants floating around.


When buying an air purifier, it’s essential to consider the machine’s noise levels.

Noise is measured in decibels, the standard noise level measurement.

Ideally, you want an air purifier that produces 50 decibels (dBa) or less.

Fifty decibels is around the volume of a normal conversation, so if you want a very silent air purifier, I suggest getting one that produces less than 30 dBA.

Air Volume

This isn’t a specification or measurement you’ll find on an air purifier.

But I chose to include it because it’s crucial when buying an air purifier.

Before you head to the market and consider different options, I suggest measuring the room’s air volume.

To do this, you must measure the room’s length, width, and height.

Then, multiply all the measurements, and that’s the room’s air volume.

So, if you have a 10-foot x 10-foot x 10-foot room, the air volume is 1,000 cubic feet.

Once you have the air volume measurements, you can compare them with the CFM to see if the air purifier is the right fit.

For example, an air purifier with a 150 CFM rating produces 9,000 cubic feet of clean air every hour (150 cfm * 60 minutes).

In this example, the air purifier can barely handle the room’s air volume, meaning you might want to get a more robust model.


Buying an air purifier doesn’t have to be complicated.

And if there’s one metric, I suggest learning before going on the market, that’s CADR.

An air purifier’s CADR shows how effectively it cleans the air.

It isn’t the perfect metric, but it does offer a lot of insight into the air purifier’s functionality.

Ideally, you want to get an air purifier with a high CADR.

But if you want to get a model that fits your needs, I suggest comparing the CADR to the size of your room.

That way, you know that your chosen air purifier is the perfect option for your space!