Guide
CADR Rating Explained: What It Means & Why It Matters
By Dr. Alex Chen · Updated 2026-03-10
CADR (Clean Air Delivery Rate) measures how many cubic feet of clean air an air purifier delivers per minute, tested independently by AHAM for three particle sizes: smoke, dust, and pollen. Smoke CADR is the most important number because it tests the smallest, hardest-to-capture particles. To match CADR to your room, your smoke CADR should be at least two-thirds of your room's square footage.
What CADR Actually Measures
CADR stands for Clean Air Delivery Rate. It measures the volume of filtered air a purifier delivers per minute, expressed in cubic feet per minute (CFM).
A CADR of 200 CFM means the purifier produces 200 cubic feet of clean air every minute. It does not mean the purifier moves 200 cubic feet of air — it means 200 cubic feet of air comes out with the tested pollutant effectively removed.
CADR is the only independently verified, standardized performance metric for air purifiers. It is the one number you can compare directly across brands because the test conditions are identical.
The Three CADR Numbers: Smoke, Dust, and Pollen
Every AHAM-tested air purifier receives three separate CADR ratings:
| CADR Type | Particle Size Range | What It Represents | Typical Relative Value |
|---|---|---|---|
| Smoke | 0.09 – 1.0 µm | Fine particles: smoke, combustion, PM2.5, virus-carrying aerosols | Lowest |
| Dust | 0.5 – 3.0 µm | Medium particles: dust mite allergens, mold spores, fine dust | Middle |
| Pollen | 5.0 – 11.0 µm | Large particles: pollen, coarse dust, pet dander fragments | Highest |
Smoke CADR tests in the most challenging particle range (0.09–1.0 µm), which overlaps with the most penetrating particle size for HEPA filters. This is why it is the lowest number and the most important for evaluating real-world performance.
Why Smoke CADR Is the Number That Matters
When comparing air purifiers, always use smoke CADR as your primary comparison metric:
- It tests the hardest particles — If the purifier performs well on smoke, it performs at least as well on everything larger.
- It represents the most harmful pollutants — PM2.5, wildfire smoke, cooking emissions, virus-carrying aerosols all fall in this range.
- It is the most conservative metric — Pollen CADR is always the highest and makes purifiers look better on paper.
CADR to Room Size: Complete Calculation
Step 1: Measure your room Room Volume = Length (ft) × Width (ft) × Ceiling Height (ft)
Step 2: Choose your target ACH
- 2 ACH: General air freshening — minimal health benefit
- 4 ACH: Standard recommendation — meaningful particulate reduction
- 6 ACH: Allergy and asthma sufferers — significant symptom relief
- 8+ ACH: Severe respiratory conditions
Step 3: Calculate required CADR Required CADR (CFM) = Room Volume (cu ft) × Target ACH ÷ 60
AHAM Shortcut: CADR should be at least two-thirds of your room area in square feet. For a 180 sq ft room: CADR needed = 180 × 0.67 = ~120 CFM.
CADR to Room Size Reference Table
| Room Size (sq ft) | Room Type | Min CADR (4 ACH) | Better CADR (6 ACH) | Best CADR (8 ACH) |
|---|---|---|---|---|
| 100 | Small bedroom, nursery | 53 CFM | 80 CFM | 107 CFM |
| 150 | Bedroom, home office | 80 CFM | 120 CFM | 160 CFM |
| 200 | Large bedroom, study | 107 CFM | 160 CFM | 213 CFM |
| 250 | Living room | 133 CFM | 200 CFM | 267 CFM |
| 300 | Large living room | 160 CFM | 240 CFM | 320 CFM |
| 400 | Large open-plan | 213 CFM | 320 CFM | 427 CFM |
| 500 | Great room, loft | 267 CFM | 400 CFM | 533 CFM |
How AHAM Tests CADR
The AHAM Verifide test uses a sealed 1,008 cubic foot test chamber (~11 × 11 × 8.3 feet). Particles are injected, the purifier runs at maximum fan speed, and particle decay is measured. CADR is calculated from the purifier-attributed decay curve.
Key test conditions:
- Maximum fan speed only — real-world CADR is lower at medium/low speeds
- New filter — performance decreases as filters load
- Sealed chamber — real rooms have air infiltration
- Empty room — real rooms have furniture affecting airflow
What CADR Does Not Tell You
- No gaseous pollutant measurement — CADR tests particulate only. VOCs, formaldehyde, and odors are not captured.
- Maximum speed only — Most people run purifiers on medium or low for noise reasons.
- No filter degradation data — A filter may deliver 10–30% less CADR by end of lifespan.
- No real-room performance — Sealed, empty test chamber doesn't represent real homes.
- No noise correlation — Two purifiers with identical CADR can have very different noise levels.
CADR vs ACH: Understanding Both Metrics
| Metric | What It Measures | Property Of | Changes With Room Size? |
|---|---|---|---|
| CADR | Cubic feet of clean air per minute | The purifier (fixed) | ❌ No |
| ACH | Full room air changes per hour | The purifier + room combination | ✅ Yes |
The relationship: ACH = (CADR × 60) ÷ Room Volume
A 200 CFM purifier delivers:
- 15 ACH in a 100 sq ft nursery (overkill)
- 6 ACH in a 250 sq ft living room (very good)
- 2.5 ACH in a 600 sq ft great room (insufficient)
Brands That Skip CADR Testing
| Brand | AHAM Tested? | Their Reasoning |
|---|---|---|
| Dyson | ❌ No | Argues CADR test conditions don't reflect real rooms |
| IQAir | ❌ No | Uses proprietary testing; claims to exceed HEPA standards |
| Molekule | ❌ No | Claims CADR framework doesn't capture PECO technology |
| Coway | ✅ Yes | Full AHAM participation |
| Levoit | ✅ Yes | Full AHAM participation |
| Winix | ✅ Yes | Full AHAM participation |
Red Flags When Evaluating CADR Claims
- Only pollen CADR displayed — The highest of the three numbers
- "Up to X CFM" — Aspirational, not tested
- No AHAM Verifide certification — Self-reported, unverified
- Room coverage without CADR — "Covers 500 sq ft" is meaningless without ACH assumption
Frequently Asked Questions
What is a good CADR rating? For a 150 sq ft bedroom, a smoke CADR of 100+ CFM delivers 4+ ACH. For a 300 sq ft living room, you want 200+ CFM. Always use smoke CADR — the lowest, most conservative number.
Does CADR measure everything an air purifier does? No. CADR measures particulate removal only — not VOCs, formaldehyde, or odors. It tests at maximum fan speed with a new filter in a sealed empty chamber.
Why does Dyson not have a CADR rating? Dyson does not participate in AHAM Verifide testing, arguing that the small sealed chamber at max speed does not reflect real-room performance. This doesn't mean Dyson purifiers are bad — it means their claims lack independent verification.
Should I buy the highest CADR I can afford? Not necessarily. Match CADR to your room size at 4–6 ACH, then optimize for noise, filter cost, and features. A slightly oversized purifier running on low speed is quieter and still delivers excellent air quality.