Clean air delivery rate (CADR) is a standardized measurement that tells you how much filtered air a portable air purifier delivers per minute, expressed in cubic feet per minute (CFM). A purifier with a CADR of 200, for example, produces 200 cubic feet of clean air every minute. The higher the number, the faster the unit removes airborne particles from your room.
How CADR Is Measured
CADR comes from a specific lab test defined by the industry standard ANSI/AHAM AC-1. The test works by releasing a known concentration of particles into a sealed chamber, then measuring how quickly those particles disappear on their own (natural decay). The particles are reintroduced, the air purifier is turned on, and the faster decay rate is recorded. The difference between the two decay rates, multiplied by the volume of the chamber, produces the CADR value. This means CADR captures both filtration efficiency and airflow in a single number, which is why it’s more useful than either metric alone.
The rating is always measured at the unit’s highest fan speed. If you typically run your purifier on a lower, quieter setting, the real-world delivery rate will be lower than the number on the label.
Three Separate Scores, Not One
Every CADR-rated purifier receives three scores: one for tobacco smoke, one for dust, and one for pollen. These represent different particle size ranges. Smoke particles are the smallest (typically 0.09 to 1.0 microns), dust is mid-range, and pollen is the largest. A single purifier can score quite differently across the three categories because filter media and airflow interact with particle sizes in different ways.
If your main concern is wildfire smoke or viral aerosols, pay closest attention to the smoke CADR. The EPA specifically recommends choosing a unit rated for smoke or labeled HEPA if your goal is filtering particles smaller than 1 micron, which includes most airborne virus-carrying droplets.
Matching CADR to Your Room Size
The EPA publishes a straightforward sizing chart for rooms with standard 8-foot ceilings:
- 100 sq ft room: minimum 65 CFM CADR
- 200 sq ft room: minimum 130 CFM CADR
- 300 sq ft room: minimum 195 CFM CADR
- 400 sq ft room: minimum 260 CFM CADR
- 500 sq ft room: minimum 325 CFM CADR
- 600 sq ft room: minimum 390 CFM CADR
The pattern is simple: multiply your room’s square footage by about 0.65 to get the minimum CADR you need. If your ceilings are higher than 8 feet, size up. A room with 10-foot ceilings holds 25% more air volume, so you’d want roughly 25% more CADR to compensate. Most air purifier packaging lists a recommended room size, but checking it against this chart gives you an independent sanity check.
CADR vs. Airflow (CFM)
Both CADR and raw airflow are measured in cubic feet per minute, which causes confusion. The difference is that raw airflow tells you how much air passes through the unit, while CADR tells you how much of that air comes out genuinely clean. A purifier with a powerful fan but a mediocre filter might move 300 CFM of air yet only deliver a CADR of 150, because half the particles pass right through. CADR is the number that matters for actual particle removal.
What CADR Does Not Measure
CADR is strictly a particle metric. It tells you nothing about a purifier’s ability to remove gases, odors, or volatile organic compounds (VOCs) like formaldehyde, benzene, or paint fumes. Research published in Building and Environment tested eight air cleaners and found that their VOC removal rates were significantly lower than their particle CADRs for every compound tested, including common household chemicals like acetone, toluene, and acetic acid. Seven of the eight units underperformed across all nine VOCs measured.
This means a purifier with an impressive CADR can still do very little about cooking smells, off-gassing from new furniture, or chemical fumes. If gas-phase pollutants are your concern, you need a unit with an activated carbon filter or similar sorbent media, and you should look for separate performance data on gas removal rather than relying on the CADR label.
How to Read the Label
The Association of Home Appliance Manufacturers (AHAM) runs a voluntary certification program called AHAM Verifide. Purifiers that carry this seal have been independently tested in a lab using the AC-1 standard, so the CADR numbers on the box aren’t just the manufacturer’s claim. The label lists three CADR values (smoke, dust, pollen) and a suggested room size. Most major brands participate, but some do not, particularly smaller or international manufacturers. If a purifier has no CADR rating at all, you’re relying entirely on the company’s own marketing for performance claims.
When comparing two purifiers side by side, compare the same pollutant score. A unit with a smoke CADR of 180 will clean fine particles faster than one rated at 140, assuming similar room conditions. For general-purpose use in a bedroom or living room, the smoke score gives you the most conservative (and therefore most reliable) estimate of performance, since those are the hardest particles to capture.
Practical Tips for Using CADR
Sizing your purifier correctly matters more than most people realize. An undersized unit in a large room will cycle the air too slowly to make a meaningful difference. If you’re between sizes, go larger. Running a bigger purifier on a medium setting often produces the same clean-air output as a smaller unit on high, with considerably less noise.
Keep in mind that CADR is tested with a fresh filter. As your filter loads up with captured particles over weeks and months, actual delivery drops. Replacing filters on the manufacturer’s recommended schedule keeps performance close to the rated number. If you have pets, live near a busy road, or run the purifier during wildfire season, you may need to replace filters more often than the standard recommendation suggests.