What is Air Purifiers CADR Rating?

You have probably seen the CADR number mentioned in the specifications of air purifiers. So what is air purifiers CADR rating really? You will find the answer here, keep reading.

What is CADR Rating?

The abbreviation CADR means Clean Air Delivery Rate. It is used as a metric for measuring the performance of air purifiers. This is essentially the total volume of air that is forced through a purifier and cleaned of pollutants. You can interpret it also as an equivalent of the volume of a completely clean air that is added to your room air.

The CADR value can be expressed in cubic inches per minute or per hour, or in cubic meters per hour. No matter what units are used, the higher the CADR number the better.

This standard is defined by the Association of Home Appliance Manufacturers (AHAM) in the U.S. So this is done by an independent and verified laboratory, and consumers can be sure that such a device will perform according to the specifications provided by a manufacturer. It is recognized as an American National Standard simply because it allows for consistent comparison between different products, and it is endorsed by the U.S. Food and Drug Administration (FDA) and the Environmental Protection Agency (EPA).

In the specifications of air purifiers you will frequently see that there are three separate CADR numbers: for smoke, pollen, and dust. In my another text I gave a few numbers for such pollutants in comparison with the sizes of viruses.

So here just to stress that smoke belongs to aerosols and it consists of tiny pieces in the range roughly 0.1  – 1 micron. On the other hand, pollen particles are usually in the range of 2 – 20 microns, but there are some that go over 100 microns.

CADR takes into account the following:

  • The volume of air that passes through the filter (which is mainly dependent on its physical size and the power if its fan).
  • The size of particles (hence the mentioned different numbers for different types of particles).
  • Filter efficiency (the percentage of the removed particles). This is almost 100% in the case of the True HEPA filters. But in the case of non-HEPA filter, you can have the volume say 100 cubic feet per minute and at the same time 80% efficiency, this would give the actual CADR value of 80.

Some typical CADR numbers

The picture below shows the CADR numbers for the LEVOIT Air Purifier. As of the moment of writing this text, this air purifier is the number 1 on Amazon in the group of best-selling air purifiers. It is included in my list of best-rated air purifiers for home use.

CADR rating for the LEVOIT Air Purifier.
CADR rating for the LEVOIT Air Purifier.

On the other hand, the CADR rating of the Hathaspace Smart True HEPA Air Purifier 5-in-1 that is included in my list of best air purifiers with ionizers is as follows:

  • Smoke: 165.
  • Dust: 160.
  • Pollen: 170.
Honeywell HFD-120-Q QuietClean Oscillating Air Purifier with Permanent Washable Filters.
Honeywell HFD-120-Q QuietClean Oscillating Air Purifier with Permanent Washable Filters.

This purifier is also in the top 10 bestsellers (as of the moment of writing this text) on Amazon.

See also the numbers for this Honeywell HFD-120-Q QuietClean Oscillating Air Purifier with Permanent Washable Filters shown in the picture here:

  • Tobacco Smoke: 110.
  • Dust: 100.
  • Pollen: 132.

So you now have some idea of what to expect from some top rated purifiers on the market.

How they test CADR?

  • The most important fact to know is that they run the device on the highest fan speed. This also implies an increased level of noise, bear this in mind. In any case, it is likely that you will be running the device on a lower speed so you can expect your effective CADR to be lower. But many of these devices have sensors to detect the air quality and then they adjust the fan speed.
  • Note also that such testing is with a new filter. We know that filters change their performance over time. So the effective CADR number may change in time.
  • The effective size of the filter also matters for obvious reasons. Larger will perform better.

What else to know

  • Quite generally, the CADR rating has nothing to do with the noise level.
  • Also, CADR tells you nothing about eventual ozone generation in a purifier. As you know there are some of these devices with a UVC light added to sterilize the air. But some amount of ozone is always produced and this is a harmful gas.
  • CADR is focused on particles only, it tells you nothing about gasses present in the air.

How to choose the right purifier for your room size

The table below gives some guidelines, on the left you have CADR numbers (in green) and the other three columns are for 1, 2, and 3 times total air changes per hour. The numbers in columns under these air changes give the corresponding room size in square feet. So this is the maximum room size that can be served by an air purifier with the CADR value given on the left.

CADR 1* 2* 3*
100 750 ft² 375 ft² 250 ft²
150 1125 ft² 563 ft² 375 ft²
200 1500 ft² 750 ft² 500 ft²
250 1875 ft² 938 ft² 625 ft²
300 2250 ft² 1125 ft² 750 ft²
350 2625 ft² 1313 ft² 875 ft²

1* 2* 3* :  This is the number of the total air changes per hour.

Here is how to read this table:

• If you want that the complete air changes in the room 3 times per hour (the last column), and you have the room of 375 ft² (the number given in bold), you will be doing fine with a purifier with the CADR number 150 (the first column).

• Obviously, you can buy a purifier with a lower CADR value, say 100, and in this case the air in the same room will be changed two times per hour, see the column under the number 2.

As mentioned above, this implies the purifier running on the highest level fan. So you can buy a device with a higher CADR, say 300, and then you will have the air changed three times per hour on a lover fan level.


In summary, although the CADR rating does not describe all important aspects related to the performance of an air purifier, this is still a good starting information when you compare various air purifiers. Check also our text about HEPA filter efficiency.

Thank you for reading. We add texts here regularly, so if you want to stay informed bookmark this site and visit it again.

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