When choosing an air purifier, one of the first numbers people encounter is CADR—but it is also one of the most misunderstood.
CADR, or Clean Air Delivery Rate, measures how quickly an air purifier can clean the air in a space. It is often used to compare different models, but on its own it does not reflect how an air purifier performs in real-world conditions over time. CADR focuses on short-term performance—how quickly clean air is delivered under specific conditions—rather than how long that performance can be maintained.
Understanding how CADR works—and how it differs from other metrics like CCM—can make it easier to choose a system that matches both the size of a space and how performance will hold over time.
What CADR actually measures
CADR reflects how quickly an air purifier removes particles from the air. It combines airflow and filter efficiency to estimate how fast clean air is delivered within a given space.
In practical terms, this means CADR indicates how quickly airborne particles can be cleared—but not how consistently that performance will hold over time.
CADR measures the removal rate of airborne particles as small as 0.09 microns to as large as 11 microns (1)(2). It reflects how filter efficiency and airflow interact within a given space, but is limited to measuring performance speed rather than long-term usage.
CADR is often presented alongside CCM, but the two metrics reflect very different aspects of performance. CADR focuses on how quickly clean air is delivered, while CCM indicates how much pollution a system can handle before its performance begins to decline.
The limitation of CADR: Speed vs long-term performance
While CADR is commonly used to compare how quickly an air purifier works, it does not indicate how performance will hold over time.
As filters load with particles and gases, airflow and efficiency can change—something CADR does not capture. Many air purifiers perform well when new but lose effectiveness as filters become saturated.
As a result, CADR alone gives an incomplete—or even misleading—picture of how an air purifier will perform outside of controlled test conditions.
CADR vs CCM: Speed vs endurance
While CADR measures speed, CCM focuses on endurance. It tracks how much pollution an air purifier can remove over time before its performance begins to decline.
CCM ratings are grouped into standardized tiers for particulate matter (P) and formaldehyde (F), which indicate how much pollution an air purifier can handle before its performance begins to decline. Higher tiers represent greater long-term filtration capacity and more stable performance over time.
| Particulate Matter | Formaldehyde | ||
|---|---|---|---|
| P1 | 3000 – 5000 mg | F1 | 300 – 600 mg |
| P2 | 5000 – 8000 mg | F2 | 600 – 1000 mg |
| P3 | 8000 – 12000 mg | F3 | 1000 – 1500 mg |
| P4 | > 12,000 mg | F4 | > 1500 mg |
In practical terms, higher P and F values indicate that an air purifier can handle more pollution before its performance drops—making these tiers a useful way to compare long-term effectiveness. For example, a system rated at P4 can remove significantly more particulate matter before performance declines than one rated at P1.
Compared to CADR, CCM reflects long-term filtration performance rather than short-term speed.
In practice, CADR reflects how quickly an air purifier performs under initial test conditions, while CCM provides clearer insight into how that performance holds up over time.
How to evaluate air purifier performance in real-world use
Understanding how an air purifier is tested can help clarify how it will perform in real-world use. If a system is too small for a space, or if performance declines over time, airborne particles may remain present. Systems with higher CCM levels are more likely to maintain consistent performance over time, which can be especially relevant for sensitive or allergy-prone groups.
CCM values reflect long-term filtration capacity. Some systems are designed to maintain performance over extended use, which is reflected in higher CCM values.
Some air purifiers are designed to perform strongly across both metrics. For example, systems using high-efficiency filtration, such as IQAir systems using HyperHEPA filtration, are designed to capture ultrafine particles efficiently while maintaining long-term performance.
Frequently Asked Questions
What is the difference between CADR and CCM?
CADR measures initial short-term performance quality, calculating the rate or speed of which airborne particulate matter is cleaned and recycled. CCM measures long-term performance longevity, calculating the sheer amount of pollutant particles that are collected by an air purifier before the device begins to lose efficiency. The key difference is the short-term versus long-term measurements.
What is more important to consider, CADR or CCM?
While both CADR and CCM are important to consider in general, CCM provides a clearer understanding of air purifier quality and filtration over time. When choosing an air purifier, CCM values give a direct ranking on which system is going to last the longest while maintaining powerful filtration.
Do all air purifiers have CADR and/or CCM ratings?
Most air purifiers should have either a CADR or CCM rating listed; however, at-home calculations and trial runs can be performed to calculate the values.
How is CADR measured by room?
A CADR rating should be 2/3 the value of the room’s square footage that the air purifier is housed in. For instance, if a room is 180 square feet, then an air purifier with a CADR of 120 should be used.
Conclusion
CADR and CCM measure different aspects of air purifier performance: speed and endurance. Looking beyond CADR to include metrics like CCM provides a clearer picture of how an air purifier will perform—not just when it is new, but over time.
