CADR (Clean Air Delivery Rate) measures how many cubic feet of filtered air a purifier delivers per minute, tested for three particle types: smoke, dust, and pollen. A purifier with a smoke CADR of 200 cleans 200 cubic feet of air of smoke particles each minute. To properly size a purifier, you need a smoke CADR of at least two-thirds of your room's square footage — so a 300 sq ft bedroom needs a purifier with at least 200 smoke CADR.
CADR is the single most important number when shopping for an air purifier. It's tested and certified by AHAM (Association of Home Appliance Manufacturers) using a standardized procedure, making it a reliable comparison tool across brands.
How CADR Works
CADR testing places the purifier in a sealed 1,008 cubic foot chamber (approximately 12 x 12 x 7 ft). Three types of test particles are introduced: smoke (0.09-1.0 microns), dust (0.5-3.0 microns), and pollen (5.0-11.0 microns).
The purifier runs at maximum speed, and particle concentrations are measured over time. The CADR value represents the effective volume of air cleaned per minute — accounting for both airflow volume and filter efficiency.
A purifier with 200 CFM of airflow but only 80% filter efficiency has a CADR of 160. A purifier with 170 CFM but 95% efficiency has a CADR of 162. CADR captures the real-world outcome: how much clean air you actually get.
The Three CADR Numbers
Each purifier receives three separate CADR ratings:
| Particle Type | Size Range | Real-World Sources | Why It Matters |
|---|---|---|---|
| Smoke | 0.09-1.0 microns | Tobacco smoke, wildfire smoke, cooking fumes, candle soot | Hardest to filter — the most telling CADR number |
| Dust | 0.5-3.0 microns | Household dust, mold spores, pet dander, fine debris | Moderate difficulty — most purifiers handle well |
| Pollen | 5.0-11.0 microns | Tree/grass/weed pollen, large dust particles | Easiest to filter — almost all purifiers score high |
Focus on the smoke CADR first. If a purifier handles smoke particles well, it handles dust and pollen even better. Smoke CADR is the most demanding test and the best indicator of overall purification capability. When comparing units, lead with the smoke number.
How to Size an Air Purifier Using CADR
The general rule from AHAM and the EPA:
Minimum Smoke CADR = Room Square Footage x 2/3
This provides approximately 4.8 air changes per hour (ACH) in a room with 8-foot ceilings, which is the minimum recommended for effective air cleaning.
| Room Size (sq ft) | Min Smoke CADR Needed | Room Type Examples |
|---|---|---|
| 100-150 | 67-100 | Small bedroom, home office |
| 150-200 | 100-133 | Standard bedroom |
| 200-300 | 133-200 | Master bedroom, large office |
| 300-400 | 200-267 | Living room, open plan area |
| 400-500 | 267-333 | Large living space |
| 500-700 | 333-467 | Great room, open floor plan |
| 700+ | 467+ | Requires multiple units or commercial purifier |
CADR is tested at maximum speed, which is usually loud. If you plan to run the purifier on medium or low speed (common for bedrooms), the effective CADR drops to roughly 50-70% of the rated value. Size up by 30-50% if you want quiet operation with adequate cleaning.
CADR Rating Scale: What's Good?
| Smoke CADR Range | Rating | Suitable Room Size | Price Range |
|---|---|---|---|
| Below 100 | Small / Entry-Level | Up to 150 sq ft | $50-$100 |
| 100-150 | Medium | 150-225 sq ft | $80-$150 |
| 150-200 | Good | 225-300 sq ft | $120-$250 |
| 200-300 | Very Good | 300-450 sq ft | $200-$400 |
| 300-400 | Excellent | 450-600 sq ft | $300-$550 |
| 400+ | Large Room / Commercial Grade | 600+ sq ft | $400-$800+ |
Top Air Purifiers by CADR (2026)
| Purifier | Smoke CADR | Dust CADR | Pollen CADR | Room Size (sq ft) | Noise (max dB) |
|---|---|---|---|---|---|
| Coway Airmega 400 | 350 | 374 | 372 | 525 | 52 dB |
| Blueair Blue Pure 211+ | 350 | 350 | 350 | 540 | 56 dB |
| Honeywell HPA300 | 300 | 320 | 330 | 465 | 63 dB |
| Levoit Core 600S | 272 | 291 | 312 | 408 | 55 dB |
| Winix 5500-2 | 232 | 243 | 246 | 360 | 56 dB |
| Coway AP-1512HH | 233 | 246 | 240 | 361 | 53 dB |
| Levoit Core 400S | 187 | 200 | 215 | 280 | 52 dB |
| Blueair Blue Pure 311i+ | 184 | 186 | 196 | 276 | 53 dB |
| Levoit Core 300 | 141 | 140 | 145 | 219 | 50 dB |
CADR vs Other Purifier Metrics
| Metric | What It Measures | Standardized? | Useful For |
|---|---|---|---|
| CADR | Clean air delivery rate (3 particle types) | Yes (AHAM AC-1) | Comparing purifiers objectively |
| Room Size Coverage | Manufacturer's claimed room size | Sometimes inflated | Quick reference only |
| ACH (Air Changes/Hour) | Times per hour room air is filtered | Calculate from CADR | Comparing to health guidelines |
| Filter Efficiency (%) | Percentage of particles captured | Varies by test method | Understanding the filter, not the purifier |
| CFM (Airflow) | Raw air volume moved per minute | Yes | Doesn't account for filter efficiency |
How to Calculate Air Changes Per Hour
If you want to verify a purifier provides adequate air changes:
ACH = (CADR x 60) / Room Volume (cubic feet)
Room Volume = Length x Width x Ceiling Height
Example: Coway AP-1512HH (smoke CADR 233) in a 15x20 ft room with 8 ft ceilings.
Room volume = 15 x 20 x 8 = 2,400 cubic feet
ACH = (233 x 60) / 2,400 = 13,980 / 2,400 = 5.8 ACH
The EPA recommends 4-6 ACH for general air cleaning and 6+ for allergy/asthma relief. This purifier provides adequate ACH for this room.
Common CADR Misconceptions
"Higher CADR is always better." Not without context. A CADR of 400 in a 200 sq ft bedroom is overkill. You'll pay more upfront, spend more on filter replacements, and deal with more noise. Match CADR to room size.
"My purifier doesn't have a CADR rating, so it's not good." Some quality purifiers (like IQAir or Austin Air) don't participate in AHAM testing. They may still perform well but lack the standardized comparison data. If there's no CADR, you're relying on the manufacturer's claims.
"CADR measures filter quality." CADR measures the combined effect of airflow plus filtration. A purifier with a mediocre HEPA filter but a powerful fan can score similarly to one with a superior filter and weaker fan.
"I need the highest CADR for wildfire smoke." For wildfire smoke, smoke CADR is the relevant number. But you also want a purifier with an activated carbon filter for volatile organic compounds (VOCs) and odors, which CADR doesn't measure.
Key Takeaways
- CADR is airflow times filter efficiency, not raw CFM. A 200 CFM fan with 80% filtration lands at CADR 160, while a 170 CFM fan with 95% filtration hits CADR 162 — that's why CADR beats CFM for comparing purifiers.
- The 2/3 sizing rule isn't arbitrary — it targets ~4.8 ACH. AHAM's smoke CADR ≥ two-thirds of room square footage formula assumes 8-foot ceilings and produces roughly 4.8 air changes per hour, the EPA's floor for effective cleaning. Taller ceilings or allergy relief (6+ ACH) require sizing up further.
- Focus on smoke CADR — it's the most demanding test and best overall indicator
- CADR is tested at maximum speed, which is usually loud. Size up 30-50% for quiet operation.
- Good smoke CADR for a bedroom: 150+. For a living room: 250+.
- ACH of 4-6 is adequate for general cleaning. 6+ for allergy/asthma sufferers.
- CADR doesn't measure gas/odor removal — that depends on activated carbon filters, which are separate
- Look for AHAM-verified CADR for reliable, standardized comparison between brands
Frequently Asked Questions
No. CFM measures raw airflow volume. CADR measures effective clean air delivery, which accounts for both airflow and filter efficiency. A purifier with 250 CFM airflow but 80% filtration has a CADR of 200. CADR is the more meaningful metric because it reflects actual cleaning performance.
Sources & References
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