CADR is a measure of how quickly an air purifier delivers filtered air. Understanding the rating helps you compare models and choose a purifier sized for your room.
What CADR means on an air purifier
CADR stands for Clean Air Delivery Rate. It describes how quickly an air purifier can remove airborne particles and deliver clean filtered air into a room. The rating is usually expressed in cubic feet per minute (CFM), although some manufacturers use cubic meters per hour (m³/h).
A higher CADR generally means an air purifier can clean a given room faster. However, CADR is only one part of the buying decision: filter type, noise, operating speed, room layout, and performance against odors or gases also matter.
What the three CADR ratings mean
Air purifiers may list separate CADR values for three particle types:
Smoke CADR: A measure associated with very small particles, including fine airborne particles.
Dust CADR: A measure of performance against larger dust particles.
Pollen CADR: A measure of performance against relatively large allergen particles such as pollen.
These ratings are not measurements of how much smoke, dust, or pollen the purifier can hold. They represent the volume of air cleaned of those test particles over time.
If a purifier lists different numbers, use the rating most relevant to your concern. Smoke CADR is often the more useful conservative reference for fine particles, while pollen CADR may be useful when seasonal allergens are the main concern.
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How CADR relates to room size
A common AHAM sizing rule is to choose a smoke CADR of at least two-thirds of the room's floor area. For example:
A 300-square-foot room calls for roughly 200 CFM of smoke CADR.
A 600-square-foot room calls for roughly 400 CFM of smoke CADR.
This rule assumes a standard ceiling height and a room that is reasonably enclosed. It is a starting point, not a guarantee of identical results in every home.
For rooms with high ceilings, frequent smoke or dust, open doorways, or heavy pollution, choose more CADR or use more than one purifier. In an open-concept area, calculate the approximate combined floor area rather than sizing the purifier for only one section.
CADR and air changes per hour
CADR can also be used to estimate how quickly a purifier cycles room air. A simple approximation is:
Air changes per hour = CADR × 60 ÷ room volume
Room volume is the floor area multiplied by ceiling height. This calculation is useful when comparing a purifier with a target air-change rate, but it assumes the purifier's published CADR applies at the speed you plan to use.
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon.com at the time of purchase will apply to the purchase of this product.
CADR is not the same as fan airflow
A fan may move a large volume of air without removing many particles. CADR accounts for both airflow and filtration efficiency.
For example, a purifier with strong airflow but a less effective particle filter may have a lower CADR than expected. A purifier with a highly efficient filter can also lose airflow as the filter loads with dust. This is why fan speed alone is not a reliable way to compare air purifiers.
Check which speed produced the CADR
The highest published CADR is commonly associated with the purifier's highest fan speed. That speed may be louder than the setting you use while sleeping or working.
When comparing models, look for:
CADR at the speeds you are likely to use
Noise ratings at those speeds
Whether the manufacturer lists separate smoke, dust, and pollen values
Whether the room-size claim is based on a recognized test method or a less specific estimate
A purifier with a slightly lower maximum CADR may be more useful if it is quiet enough to run continuously. Running a purifier consistently at a moderate speed can be more practical than running a louder model only occasionally.
What CADR does not tell you
CADR primarily describes removal of airborne particles. It does not fully describe:
Odor or gas removal: Particle CADR does not measure how well a purifier removes cooking odors, smoke gases, or volatile organic compounds. These require an appropriate activated-carbon or other gas-phase filter, and the amount of carbon matters.
Filter life: A high CADR does not tell you how long the filter will last. Dusty or smoky conditions can load a filter quickly.
Noise: CADR does not indicate how loud the purifier is.
Energy use: A larger or faster fan may use more electricity.
Real-world room performance: Open doors, leaks, high ceilings, and poor placement can reduce effective cleaning.
Protection from every pollutant: CADR is not a certification that a purifier removes microbes, gases, or all types of indoor contamination.
CADR versus the advertised room size
Manufacturers may publish a recommended room size, but those claims are not always based on the same target air-change rate. Compare the actual CADR when possible rather than relying only on labels such as “covers 1,000 square feet.”
Also check whether the stated coverage assumes a very low air-change target. A purifier rated for a large room may clean that room slowly, especially if the room is open to other spaces. CADR gives you a more useful basis for comparing models from different brands.
How to choose using CADR
Use this process:
Measure the room's floor area. Multiply length by width.
Consider the ceiling height and layout. Increase the target if the ceiling is high or the room opens into other areas.
Choose the relevant particle rating. Smoke CADR is a useful conservative reference for fine particles; pollen CADR matters for larger seasonal allergens.
Compare CADR, not only advertised coverage. Check whether the rating is listed in CFM or m³/h.
Check operating noise. A purifier must be comfortable to run at the speed needed for the room.
Plan for filter replacements. Confirm that replacement filters are available and that the purifier has a filter-change indicator or a clear maintenance schedule.
To convert approximately between units, 1 CFM equals about 1.7 m³/h. A CADR listed as 200 CFM is therefore about 340 m³/h.
The practical takeaway
CADR is the best quick indicator of an air purifier's particle-cleaning capacity. Use the smoke CADR as a conservative comparison, aim for at least about two-thirds of the room's square footage in CFM, and choose additional capacity for high ceilings, open layouts, or heavy pollution. Then check noise, filter availability, energy use, and carbon filtration if odors or gases are part of the problem.
A higher CADR generally cleans particles faster, but it may also mean more noise, higher energy use, or a larger unit. The best choice has enough CADR for the room at a speed you can run consistently.
Which CADR rating should I use for allergies?
Look at the pollen CADR for larger seasonal allergen particles, but smoke CADR is also a useful conservative measure of fine-particle cleaning. A true high-efficiency particle filter and adequate room coverage matter more than the label alone.
What CADR do I need for a 300-square-foot room?
A common sizing rule suggests at least about 200 CFM of smoke CADR for a 300-square-foot room with a standard ceiling. More capacity may be appropriate for high ceilings, open layouts, or heavy smoke and dust.
Does CADR measure odor removal?
No. Particle CADR does not measure removal of odors or gases. For those concerns, check for an activated-carbon or other gas-phase filter and consider how much filter media the purifier contains.
Is CADR the same as airflow?
No. Airflow describes how much air the fan moves, while CADR reflects the amount of particle-cleaned air delivered. Filtration efficiency affects CADR, so two purifiers with similar airflow can have different CADR values.
