What Is A CADR Rating In Air Purifiers? A CADR Air Purifier Facts Guide

Air purifiers are pretty simple in how they work, but some also include a rating to help you compare them during shopping and find the best match for your space.

But what is a CADR rating in air purifiers? Where does it come from, and how does it help you?

In this article, I’ll cover:

  • What a CADR is and why it matters
  • Good CADR ratings
  • A quick rule of thumb to help you when shopping
  • …and more!

What is a CADR rating in air purifiers?

Example CADR rating label with notes explained

Shown here is a standard CADR label illustrated. CADR labels are usually (but not always) printed on the box of an air purifier so you’ll know their air cleaning effectiveness based on testing how well they perform.

The Clean Air Delivery Rate (CADR) is an industry-standard rating, based on testing in a lab, that describes an air purifier’s air cleaning effectiveness for particles from 0.10 to 11 microns in size.

Note that a micron a microscopic size; a micron is one millionth (1/1,000,000) of a meter in size, with larger particles like dust being several microns in size.

While not mandatory in the industry, it’s often used by better air purifier manufacturers to provide buyers with a way to choose the best air purifier based on proven numbers, rather than advertising claims. The higher the CADR rating, the faster the unit can clean your air.

Basically, the idea behind it is that manufacturers can use the independent test company to verify the performance of their products. If the claimed air cleaning performance isn’t met, they’re not allowed to display the certification label on the product box.

Long story short, this all means that the CADR rating will help you pick an air purifier that’s right for the room you use it in, your air quality problems, helping you to buy with confidence based on a reliable & proven standard.

How is the CADR rating measured?

CADR rating test measurement setup diagram for air purifiers

The CADR rating is measured by using an industry-standard way of testing an air purifier inside a fixed volume of air, much like a room in real life. An air purifier is tested in a sealed lab room that’s 1,008 cubic feet (28.3 cubic meters) in volume for 20 minutes and the contaminants in the air are measured at each stage of the test.

How is CADR calculated?

CADR numbers are basically found using the “air cleaner turned on removal rate” minus the “natural decay rate of the air particles” multiplied by the test chamber’s volume (1,008 cubic feet). Or, expressed as a formula:

CADR in cfm = [Rate air cleaner on – natural decay] x 1008

(Note that in countries that use metric measurements, volume and CFM in meters are used).

This means the test ratings are based on how much air the purifier can move (measured in cubic feet per minute [CFM]) and how many particles they remove from the air, not counting the natural amount of particles that fall to the floor. That’s so that the test is more accurate.

Knowing the CFM, a formula is used to then provide a recommended room size the purifier will work well for.

Smoke, pollen, and dust CADR scores

Three common types of air particles are tested and the rate at which an air purifier can remove them is measured.

These are:

  • Smoke particles (the smallest particles an air purifier will deal with)
  • Dust
  • Pollen

Because they behave differently (dust and pollen fall to the floor faster while smoke particles behave differently), they’re graded separately since how efficiently they’re removed is often different.

CADR rating standards are provided by an organization called the AHAM for air purifier product makers who participate in their program and submit products for testing.

Quick fact: Of the three listed above (and of nearly all common air contaminants), smoke particles are the smallest and also some of the most dangerous.

What is the AHAM organization?

AHAM logo

The Association of Home Appliance Manufacturers (AHAM) is a voluntary group of appliance product makers that brings them together in a single unified organization. They represent companies with a wide range of products – not just air purifiers.

For example, cooking & heating appliances, washing machines, suppliers to the industry, and more. The AHAM provides a way to maintain standards and reliable guidelines that appliance buyers can use in order to know they’re getting what they’re paying for, in addition to standardizing some things in the industry in general.

Do all purifiers sold have a CADR rating?

Do all air purifiers have a CADR rating

No, CADR ratings are not provided for all air purifiers sold. Only for those that the manufacturer has submitted for AHAM testing and have passed the requirements.

That’s usually the larger manufacturers such as Levoit, Honeywell, Winix, GermGuardian, and others. It’s rare to find “off-brand” air purifiers with CADR ratings listed. If the AHAM does not provide them, they may not be legitimate.

Example of a CADR rating on an air purifier box

Example of a CADR rating label, as shown for a Honeywell air purifier.

Before shopping for an air cleaner, it’s important to remember that unless CADR ratings are provided their claims about air cleaning effectiveness may not mean much.

Are CADR ratings required by law?

No, CADR ratings are voluntary. Air purifier makers are also not required to be members of the Association of Home Appliance Manufacturers.

United States law doesn’t require air cleaners to have a proven test lab rating. However, note that the tests used by the AHAM are based on some recommendations & consultation with the United States government.

How CADR ratings are helpful

How are CADR rates helpful section image

The Clean Air Delivery Rate is very helpful for comparing air purifiers when shopping and finding the most effective one for your air quality problem.

For example:

  • When choosing between an air purifier without a CADR rating provided and one with the CADR provided.
  • Two similar room size purifiers – the one with the higher CADR will be a better choice.
  • Choosing the purifier with a higher CADR rating for smoke, dust, or pollen (as needed for your situation).

One of the issues with CADR ratings is that because of the requirements for airflow, a purifier with higher ratings for one contaminant type will usually have lower ratings for the others. For example, better smoke particle cleaning requires a slower fan speed meaning the other 2 ratings (pollen & dust) will be lower.

One reason is that smoke particles fall to the floor slower than dust, for example. Therefore if a slower fan removes smoke particles better, the reduced dust won’t be as high (since a higher fan speed would remove more dust).

What is a good CADR rating?

CADR ratings are affected by the size and airflow of the purifier, meaning that larger, more powerful purifiers will have a better rating. That’s because it’s impossible for a smaller room air cleaner to move as much air as a larger one with a bigger, more powerful fan.

Additionally, larger purifiers also have more filter square inches therefore, they can capture more particles as air passes through them.

Here’s a table with examples of some typical (and popular) air purifiers along with the CADR ratings you can expect and are considered good. When choosing a purifier, it should have CADR ratings about the same or higher.

Purifier/Room Size Typical CADRs Notes
Small room (78 sq. ft.) 56 / 76 / 50 Affordable, but not very effective at cleaning the air. I recommend at least a medium-room purifier instead.
Medium (167 sq. ft) 108 / 118 / 125 Good for small rooms or rooms moderate medium rooms. One of the most popular sizes.
Medium-large (310 sq. ft.) 200 / 190 / 180 Very good for medium/medium-large rooms.
Large (360 sq. ft.) 232 / 243 / 246 Very good. Many have a special high-speed fan mode. Noisy fan on the highest speed.
Large/Extra-large (465 sq. ft.) 300 / 320 / 300 Very good. Many have a special high-speed fan mode. Noisy fan on the highest speed.

I recommend the following CADR ratings as good minimum choices:

  • Small room purifiers: I actually don’t recommend these as they can’t move much air. My advice is to use at least a medium-room sized purifier.
  • Medium room size purifier: Around 100+ or higher CADR.
  • Medium-large room size purifier: 180-200 or above.
  • Large: About 230 or higher is a good choice.
  • Large/extra-large room purifier: around 300 or higher is good.
Note: You can use a larger room size purifier than required for the room you’re using it in. A purifier with a higher CADR and higher airflow rate (CFM) will clean the air even faster and more times per hour.

What is a HEPA filter?

Diagram showing HEPA filter efficiency

High-Efficiency Particulate Air filters are responsible for trapping airborne nasties in your home as a purifier works. They’re very effective when used in a well-designed purifier.

High-Efficiency Particulate Air (HEPA) filter describes a type of filter designed to meet efficiency and air purification quality levels set by the United States Department of Energy. They’re made of a very dense fiber-like material that’s white in color.

To meet the standard a filter must be able to remove 99.97% of airborne particles that enter it down to 0.3 microns in size.

A filter’s efficiency refers to how many particles it can trap and remove from the airflow that passes through it. At 99.97%, for every 10,000 particles flowing into it, only about 3 escape. That means nearly all particles passing through the purifier are permanently removed from the air around you.

CADR rating frequently asked questions (FAQ)

CADR frequently asked questions section image

Here are some of the most commonly searched questions (and answers) people search for. I hope they’re helpful for you, too!

Q: What is a good CADR rating for air purifiers?

A: I recommend the following CADR ratings as good minimum choices:

  • Small room purifiers: Not recommended as they can’t move much air. For best results, use at least a medium-room sized purifier for small rooms with a CADR of 100+.
  • Medium room size purifier: Around 100+ or higher CADR.
  • Medium-large room size purifier: 180-200 or above.
  • Large: About 230 or higher is a good choice.
  • Large/extra-large room purifier: around 300 or higher is good.

Q: Is higher CADR better?

A: Yes, generally speaking, a higher CADR rating is better. Note that purifiers with a higher smoke CADR rating have somewhat lower dust & pollen ratings, and vice versa. Higher CADR ratings are typically found on larger purifiers recommended for larger room sizes and lower CADRs for smaller purifiers.

Q: Is CADR the same as CFM?

A: No, the Clean Air Delivery Rate (CADR) is a lab-tested measurement of the number of contaminants a purifier can remove from a sealed room. This is a measurement of cleaning efficiency. Cubic Feet per Minute (CFM) is a measurement of the volume of air a purifier can move, not its cleaning performance. However, CFM does affect the clean air delivery rate (CADR), where a higher CFM means more cleaning effectiveness.

Q: What CADR do I need?

A: The CADR depends on the size & capacity of the purifier, as they’re recommended for different rooms sizes based on test data and their CFM airflow rate. I recommend a CADR of at least 100 for small or medium sized rooms, around 200+ for medium-large, 230+ for large rooms, and 300 or above for extra-large rooms.

Grant Williams

About the author

Grant is a professional engineer by trade and has experience with both maintenance and do-it-yourself home projects. He enjoys sharing his expertise & ideas with others to help them improve their comfort and quality of life. Read more »

Your comments are welcome!

  1. An excellent explanatory article! Thank you very much.
    What do you think about possibility of re-using HEPA-filters by cleaning them with a vacuum-cleaner?

    • Hi Dmitriy. You can definitely do that to remove contaminants and other things trapped on the outside. It can’t remove tiny particles caught within the filter but can help you extend the life of it. Especially in cases like dust, hair, etc., etc.

      In fact, some brands have models where they mention doing so for that very reason. Best regards!

  2. Thank you very much for your reply!
    Also could you please check if I got the CADR meaning right?
    I have 2 questions in particular:  

    1) In your article, on the first image with an example of a CADR rating label, there are numbers 232, 243, and 246. 
    The unit for those numbers is CFM, right? Is it correct to read as 232 CFM, 243 CFM, and 246 CFM?

    2) If I want to translate that label’s CADR units into metric system, would it be correct like this: 
    360 sq. feet = 109.7 sq. meters
    232 CFM = 6.5 CMM (m3/min)
    243 CFM = 6.88 CMM
    246 CFM = 6.96 CMM?

    • Hi there. Well, technically the CADR really isn’t exactly the same as the airflow (cubic feet per minute) and I can see why it’s a bit confusing, especially when you consider CFM versus cubic meter per hour. Good question!

      It’s easier to think of the CADR rating as how much air the purifier can move in a room, removing “some amount” (depends on its efficiency) of particles while it works. It will tell you “how much air the purifier can clean in a room per hour” a real-world situation, in other words. And where the more the better of course.

      So you can take the CADR rating with imperial units (cubic feet per MINUTE) and multiply by 1.699 to get the same in cubic meters per hour. It’ll be a larger number since we’re having to convert to “per hour” for the M^3/hr.

      For cubic meters per minute, yep, you were right! You can just multiply the CADR by .0283168 (or close to that value). Best regards and I hope this helps!

      I’ll work on updating the article to help clarify all this. :)

  3. May I ask another question?
    In other countries air cleaner manufacturers don’t use AHAM’s methodology for determining CADR rates.
    Instead they just put wording like this: “This purifier unit is suitable for a 47 sq. meters room”.
    And consumers mostly just don’t have any other choice but to make purchase decisions based upon such subjective wording.
    I am thinking about any reasonable formula for making a selection of purifiers for particular room size, based on such subjective ratings.
    For example, adopting the AHAM 2/3 rule in the following manner: “If the manufacturer suggests 47 sq. meters, better results will be for rooms with size of 31.3 sq. meters” (2/3 of 47). And in reverse, “if you shop for a purifier and your room size is 31 sq. meter, it’s better to buy a unit for 47 sq. meters.”
    Could you please tell your opinion about the suitability of such an approach?
    Or maybe you could suggest something else?
    Thank you!

    • Hi Dimitry. (Note: I’m sorry for the delay there seems to be a technical problem as I wasn’t notified of your additional comment etc. I’ll try to figure out what’s going on.)

      Regarding your question, I think there’s a misunderstanding. The AHAM is suggesting you pick an air purifier with at least a CADR that’s 2/3 or better for a given room size. Not the other way around. For example, If you have a room that’s 15 x 25 feet (4.57 x 7.2 m, or 34.8m^2), you’d want an air purifier rated for 34.8 x .66 = 22.7 or better.

      They’re basically giving a general guideline based on *typical* users at home, not extreme cases like heavy smoke or something hard to deal with/out of the ordinary. An air purifier with 2/3 CADR of your room size will be able to clean the air relatively quickly without an issue for average users (as opposed to one that can’t move enough air in a room the size of yours or cannot efficiently clean the air, like small room purifiers with a poor airflow rate).

      The 2/3 rule means it’s good. An air purifier with an even higher rating is even better, but not really necessary. It’s “icing on the cake” as we say. I hope that helps. :)

  4. Thank you
    and how would you calculate the % of actual reduction of 100 % of a given amount of contaminant in the room over a 20 minute period or 1 hour period.
    Is such a number obtainable from the CADR reading and …it is a relevant number that is used by people.

    Thank you

    • Hi David. Well, for common particles, smoke, and dust they can remove, we know it will be about 99.97% that will be removed after a full cycling & cleaning of the room’s air.

      Based on the room size you can calculate that approximately. If you know the room size in cubic feet you can estimate how long it takes for a full cycle of the room: (room_size in ft^3)/(CADR) = x hours to clean the room fully.

      You could then divide the time you’d like to use (ex: 20 minutes, 60 minutes) by that number to get a ratio or percentage. For example, let’s say you have a unit with a CADR of 125 and your room size is 250ft^3. That would be 250/125 = 2h to clean the room once (120 minutes).

      So 20 minutes/120 minutes = 0.167 => 16.7% cleaned. I hope that helps!


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