With so many air purifiers out there these days, finding the “right” one can feel like a matchmaking marathon. Even if a particular model complements your home’s aesthetics and has all the bells and whistles, it may still not be a good fit for your specific-sized space. The likely reason? An insufficient “Clean Air Delivery Rate” or CADR. This term is usually displayed on the device’s packaging, alongside three numbers divided by back-slashes. But unfortunately, most shoppers skim past it or don’t think much of it, unaware that CADR is a tremendously crucial factor to consider when buying an air purifier. Before we explain why that is, let’s look at what CADR means.
Clean Air Delivery Rate (CADR) is a numerical rating that indicates how quickly an air purifier cleans the air in a room. More technically, CADR reflects, in cubic feet per minute (cfm), the volume of air the purifier filters every minute to remove particles of three different sizes, namely:
Generally, the higher the CADR number for a particular pollutant, the faster the purifier can filter it and the larger the area it can serve, according to an air purifier guide from the U.S. Environmental Protection Agency (EPA).
The CADR rating for an air purifier is determined through standardized laboratory tests that follow rigorous protocols. Crucially, these tests are performed in third-party facilities certified by the Association of Home Appliance Manufacturers (AHAM). AHAM is an independent organization that developed the CADR rating standards and manages the CADR testing and certification program.
CADR testing isn’t mandatory, so not every air purifier has a CADR rating. But for those manufacturers who send their purifiers for analysis and certification, the “AHAM Verifide®” CADR testing process typically involves the following steps:
An air purifier’s CADR values are calculated by subtracting the particle reduction with the air purifier turned off from the amount reduced when the unit is turned on, times the size of the room.
CADR = [Rate of particle removal (RPR) with purifier ON – RPR with purifier OFF (natural decay)] x 1,008 ft3
Once AHAM determines the air purifier’s air cleaning performance in the space, they designate the unit with a three-number rating for each type of contaminant, expressed in cfm. The AHAM-certified CADR rating for air purifiers tops out at 450 cfm each for pollen and smoke and 400 cfm for dust. Notably, air purifiers with the highest efficiency filters and an efficient and effective airflow tend to achieve the best CADR ratings.
Now that you know what CADR means and how it’s tested, the next question is: why exactly does CADR matter? In this section, we’ll answer that question by laying out some of the top benefits of CADR ratings in air purifiers.
Without knowing and understanding an air purifier’s CADR rating, you might be more compelled to purchase a model based solely on manufacturers’ claims, which aren’t always accurate. A CADR rating provides a neutral, measurable, and consistent way to assess an air purifier’s cleaning power and compare units across different brands and models, including those that have undergone the same testing. Being able to tell how well a specific purifier might work takes the guesswork and marketing hype out of the buying process, which can help you find the best air purifier for your needs.
Learn where to place an air purifier for the best air quality.
A key focus when researching top-rated air purifiers is ensuring they have enough power for the specific space in which they’ll be placed. An underpowered unit will struggle to clean the air fast enough to make a positive difference, while having an unnecessarily big or overpowered unit in a small room can be a giant waste of energy and money. CADR solves this dilemma by providing a benchmark for an air purifier’s effectiveness in relation to your room size.
If you or another household member is sensitive to specific household allergens, such as dust mites, pet dander, or pollen, or lives with a smoker, a CADR rating lets you know if a particular air purifier can effectively remove that particular allergen. A higher CADR rating indicates that the purifier can quickly capture those allergy-triggering particles before they can cause flare-ups. It also means the room’s air will contain much lower levels of the specific allergen(s), creating a safer, healthier indoor environment for those with asthma or allergies.
Discover the best air purifiers for asthma and which air purifiers help reduce allergies.
Once you know an air purifier’s CADR rating (in CFM) and the accompanying suggested room size, you can determine its Air Changes per Hour (ACH). The ACH rating measures how often the air in a room is “exchanged” for new, fresher air every hour. The higher the ACH, the more frequently and effectively the purifier “refreshes” the air and keeps up with unfiltered air entering the room. So, it’s good to know what an air purifier’s ACH is before buying one, and knowing the CADR is needed to calculate it.
The ACH for an air purifier is typically displayed as a single number followed by an “x”, such as “5x”, “6x,” and so on. If it isn’t shown, you can calculate the purifier’s ACH by dividing the unit’s CFM by your room’s volume (length x width x ceiling height, in cubic feet), then multiplying it by 60.
To calculate ACH, use this formula: ACH = (CFM x 60) / Room Volume (in ft3).
AHAM recommends that an air purifier’s CADR be at least two-thirds of the room’s area. To measure the square feet of a room, use a laser measure or a good old-fashioned tape measure to obtain the dimensions for the room’s length and width and plug them into the formula below.
Room size (in square feet) = room length x room width
So, if your room has a length of 15 ft and a width of 20 ft, its square footage would be: 15 x 20 = 300 ft2. And since two-thirds of 300 is approximately 200, you’d need an air purifier with a smoke CADR of at least 200 cfm for your room.
For wildfire smoke (which can quickly fill a room with dense, harmful particles), AHAM says a purifier’s Smoke CADR should be the same as the room’s square footage. In some instances, however, you may need a higher CADR, such as in spaces where many people gather, when indoor pollution reaches above-normal levels, or if the room’s ceiling is taller than 8 feet.
For all its remarkable benefits, CADR is not the be-all, end-all when evaluating air purifier performance. One reason is that CADR only indicates the purifier’s air-cleaning capacity at its highest airflow setting, which is the noisiest and uses the most power. The same air purifier running at lower fan speeds won’t achieve those higher CADR ratings. Also, a CADR reading doesn’t account for gases, odors, volatile organic compounds (VOCs), and other pollutants not counted as particles, nor does it discern between air purifiers with UVC light and other air purification methods. Therefore, if any of these non-particle pollutants are a potential concern in your home or office, a CADR rating should not be the only metric you use when picking out an air purifier.
TrustedAir’s TruFlow Series Smart HEPA Air Purifier boasts impressively high CADR ratings for smoke (~230 cfm), dust (~240 cfm), and pollen (~260 cfm), delivering clean, filtered air to rooms up to 1,900 square feet in under an hour. It uses an advanced three-stage filtration process with a washable prefilter to block larger pollutants, a True HEPA filter that effectively captures 99.97% of particles down to 0.3 microns, and an activated carbon filtration to neutralize odors, gases, and VOCs. Pair that with intelligent air tracking, whisper-quiet Sleep Mode (26 decibels), app connectivity, and other smart features, and you have a well-rounded, top-performing purifier suited for virtually every room.
Though CADR shouldn’t be the only thing you look at when buying an air purifier, it provides meaningful insights into the unit’s air-cleaning capabilities. It tells how quickly the unit will clear the air of various-sized indoor pollutants, such as smoke, dust, and pollen. By understanding CADR ratings and their calculations, you’re a step closer to finding an air purifier that fits your room size and produces the best air quality.
But as always, if you need more help choosing the best air purifier for your home or business, contact TrustedAir today. Our experts will happily answer your questions and help you select the right solution for your air purification needs.
CADR (Clean Air Delivery Rate) is the volume of clean air an air purifier produces each minute, factoring both filter efficiency and airflow. It’s reported in CFM (cubic feet per minute) for three particle types: smoke, dust, and pollen under the AHAM AC-1 test method.
Use the smoke CADR. It reflects the smallest particles (roughly 0.1-1 μm), which best represents wildfire smoke and typical indoor fine PM2.5.
For an 8-ft ceiling, a quick rule is:
Recommended room size (sq ft) ≈ smoke CADR × 1.55.
For other ceiling heights, adjust by multiplying by (ceiling height ÷ 8).
Example: if smoke CADR = 200 CFM and ceiling = 9 ft → room size ≈ 200 × 1.55 × (9/8).
Air changes per hour (ACH) can be estimated from CADR with:
ACH ≈ (CADR × 60) ÷ room volume, where room volume = (length × width × ceiling height) in cubic feet. Higher ACH means faster whole room cleaning.
Not necessarily. HEPA refers to filter efficiency, while CADR depends on efficiency × airflow. A purifier with an ultra-tight HEPA filter but weak airflow can have lower CADR than a well-designed unit balancing both.
CADR is measured at the purifier’s maximum fan speed in a controlled test room. Real homes vary (doors open, furniture, leaky rooms), and lower fan settings will reduce effective CADR. Use CADR to compare models, then set expectations based on your actual fan speed and layout.
