What Is CADR?

If you’ve recently gone shopping for a new air purifier for your home, you may have run into a rating measurement next to the acronym CADR.

However, you may not have known what this measurement stands for, and whether you should even pay attention to it when shopping for these kinds of products.

Understanding this rating can be a bit tricky, and may complicate the process of shopping for air cleaning units. If we put it simply, the CADR rating stands for the air purifier’s efficiency. If you compare the CADR ratings on different units, it can help you pick the one that will have the optimum effect on your indoor space.

In this article, we’ll give our best to give you all the information we have about the CADR ratings and their meaning, and help you search for your optimal air purifier more easily.

CADR Rating – Meaning

CADR acronym stands for Clean Air Delivery Rate. This metric was developed in order to assess the performance of air purifiers made for residential spaces. Therefore, if you are buying an air purifier for your home, the CADR rating should be something that concerns you.

CADR basically reflects how many cubic feet of air is being cleaned of certain size particles per minute. There are three types of particles on which this was being tested: pollen, smoke, and dust, each representing one of the three particle size groups, and having its own CADR scored assigned.

When you’re shopping for an air purifier, the CADR ratings are one of the most important things to consider. Before them, we use to rely on CFM rating (cubic feet per minute), which is somewhat similar, however, CADR ratings are actually much better effectiveness indicators on the amount of air the machine can clean in a given time unit.

Verification of Air Cleaning Products Using CADR

The association of air cleaning products (AHAM) manufacturers uses a standardized procedure for verifying the effectiveness and quality of air purifiers. The unit is usually placed in a test space of 1008 cubic feet, which corresponds to a 12 square foot room with a 7-foot tall ceiling.

Then, devices for monitoring and measuring the amount of pollen, smoke, and dust in the air are placed inside the space, and the air purifiers are switched on at full speed. Depending on the amount of time needed for the air purifier to clean the air, the CADR rating is being calculated and assigned to the particular device.

How to Determine Which CADR Do You Need?

While at first, it may seem logical to simply purchase the air purifier with the highest CADR score, this might be too much for your target space.

The logic behind CADR is that you should first calculate the size of your space and then match it to the appropriate CADR rating. The ideal CADR rating is some ⅔ of the size of your room’s area.

If you’re not sure how to calculate the size of the area of your room, here’s some advice: get a measuring tape, measure the width and the length of the floor/adjacent walls. Then, multiply the two measures and the number you get is the number of your area’s squared feet. Multiply that by 0.67 (approximately ⅔), and you’ll get the exact measurement for your desired CADR rating.

Let’s look at an example. If one wall is 10 feet wide and the other wall is 12 feet wide, your area size is 120 square feet. Multiplied by 0.67 is 80.4. This means that your desired CADR rating for this particular room is around 80.

The Benefits of Using the CADR Measure

There are many benefits to relying on the CADR metric. First, it allows the consumers to compare the air cleaning products by at least three parameters: filter efficiency, airflow, and price.

CADR is basically a product (multiplication) of CFM (airflow measure) and air filter efficiency. If the CFM of a filter is 200 and it’s 100% efficient, the CADR measure will be 200. If the efficiency is 50%, the CADR will be 100.

If you know this simple math behind the CADR measure, you’ll not be easily tricked when shopping for an air purifier.

A unit can have a very high efficiency of the filter, but a low airflow and the CADR score will actually be quite informative of this imbalance.

Very often, manufacturers use the counting of the particles are a method of revealing the efficiency of their air cleaning product. This kind of test is valid, however, it doesn’t contain other important variables such as noise production and airflow, and as such, can be seen as deceiving for the buyer. The number of removed particles may seem like an appealing measure, but CADR is more reliable as it gives you that information and additional information about airflow.

Is CADR Measure for a Unit Constant or Variable?

CADR metric provides a lot of useful information when you’re purchasing a brand new air purifier. However, if you want to buy a second-hand product, the situation is a bit different.

It’s almost impossible to fully prevent any device from wear and tear. These machines collect particles from the air, and despite your maintenance efforts (cleaning, replacing the filter, etc), their efficiency will reduce over time, and thus their CADR rating.

If you want to purchase a used air purifier, and the seller is trying to use the CADR measure as an argument to convince you into buying, you should be aware that this rating has lowered if the unit has been used.

Also, your own unit will slowly lose a tiny percentage of its rated power and effectiveness, the more and longer you use it.

Also, if you run the purifier at a lower fan speed, you will get a lower immediate efficiency than suggested by the CADR rating. This is because the CADR rating is measured and calculated for each unit when they are running at full fan speed. If you don’t want the unit to be activated at its maximum fan speed, do not expect its maximum performance.

Furthermore, the CADR measure is formulated with a brand new, unused, clean filter that will probably work very well in the testing situation. However, soon after the testing, it may drop in performance. You should have your filters regularly replaced for the purifying unit to maintain its efficiency. Also, larger filters that have lots of filter media have a significantly better performance than smaller and thinner filters. Check the box or product description for this kind of information before purchasing the unit.

CADR Does Not Involve…

CADR unit does not factor in the noise levels produced, so you may also want to find this information separately, as it may affect your decision when buying the unit. Loud units are not very useful, as they disrupt the quality of life at home. If you have small children that take naps during the day, a loud air purifier might make it difficult for them to fall asleep.

Finally, the CADR measure doesn’t tell you anything about the safety of the product. It does not involve information about the potential production of ozone, how reliable the motor is, or how much energy it uses. Before making a purchase, you may want to check all this.

Some purifiers contain ionizers that produce harmful amounts of ozone, so you want to avoid that. Also, you want to consider the long-term operating costs in terms of the cost of replacement filters and energy consumption.


To sum up, CADR ratings are one of the most informative and reliable ways to compare air purifiers. The rating gives you information about how much clean air is being produced when the fan of the unit is set up to the highest speed.

This measurement is important if you want to know more about the performance of your air purifier. It gives you information about whether the strength of the unit is sufficient for the area you live in. If there is not enough airflow, the unit won’t clean your room’s air efficiently.

In general, the larger the air purifier, the better the CADR rating. Simply put, larger filters and more powerful fans have better odds of cleaning the indoor air more efficiently. Also, air purifiers that are shaped like a tower have a better CADR score than those that have a box shape.

Finally, the CADR measure is focused on particles mainly, so it doesn’t give so much information about the removal of gases. It also doesn’t say much about the amount of noise produced, reliability, or energy efficiency, so you’ll need to check for this information separately.