CADR is the single most useful number on an air purifier's spec sheet — and the most misunderstood. This guide explains exactly what it means, how AHAM tests it, what the three scores represent, and how to use the number to match a purifier to your room.
Want to skip the explanation and size a purifier for your room right now? Use our CADR calculator →
CADR Ratings for Popular Air Purifiers
Smoke CADR is the conservative sizing benchmark — it reflects worst-case filtration performance. Data source noted per model.
| Model | Smoke CADR | Dust CADR | Pollen CADR | AHAM Coverage | Data Source | Price |
|---|---|---|---|---|---|---|
| Coway AP-1512HH Mighty | 233 CFM | 246 CFM | 240 CFM | 361 sq ft (4.8 ACH) | AHAM Verifide | Check Price |
| Levoit Core 600S | 391 CFM | 398 CFM | 436 CFM | 606 sq ft (4.8 ACH) | ENERGY STAR | Check Price |
| Levoit Core 400S | 231 CFM | 240 CFM | 259 CFM | 358 sq ft (4.8 ACH) | AHAM Verifide | Check Price |
| Winix 5500-2 | 232 CFM | 243 CFM | 246 CFM | 360 sq ft (4.8 ACH) | AHAM Verifide | Check Price |
What Is CADR?
CADR stands for Clean Air Delivery Rate. It is a measurement developed and standardized by AHAM (the Association of Home Appliance Manufacturers) of how much filtered air an air purifier delivers per minute. The unit is CFM — cubic feet per minute.
The critical word is clean. CADR does not measure total airflow through the machine. It measures the rate at which contaminant-free air exits the purifier. A unit that pushes 400 CFM of air through a filter that only removes 50% of particles delivers a CADR of roughly 200 CFM — because only half the outgoing air is actually clean. That distinction is why CADR is more useful than raw fan airflow specs.
A purifier with 300 CFM fan airflow and True HEPA efficiency (99.97% of particles at 0.3 microns) delivers a CADR approaching 300 CFM for particles at that size range. A "HEPA-type" filter at 85% efficiency with the same fan delivers roughly 255 CFM CADR. Same fan speed, meaningfully different clean air output.
The Three CADR Scores: Smoke, Dust, and Pollen
CADR is reported as three separate scores, each using tracer particles of different sizes in the AHAM AC-1 test:
- Smoke CADR — uses particles in the 0.09–1.0 micron range. The smallest particles and the hardest for filters to capture. Smoke is usually the lowest of the three scores.
- Dust CADR — uses standardized test dust in the 0.5–3 micron range. Mid-range difficulty.
- Pollen CADR — uses particles in the 5–11 micron range. Large particles, easiest to filter. Typically the highest score.
The three scores diverge most on units with weaker filter media. A True HEPA filter captures all three size ranges at very high efficiency, so smoke/dust/pollen CADR scores tend to be relatively close. A "HEPA-type" filter at 85–90% efficiency struggles more with the smallest smoke particles, so the smoke score drops noticeably below pollen.
How AHAM Tests CADR (the AC-1 Standard)
AHAM CADR testing is conducted under the AHAM AC-1 standard in a sealed 1,008 cubic foot chamber (roughly 12 × 14 ft with 8-foot ceilings). The chamber is seeded with tracer particles at a known concentration. The purifier runs at its highest fan speed for 20 minutes. Particle concentration is measured before and after, and CADR is calculated from the decay rate.
The test formula:
CADR = (k − n) × V
Where k is the particle decay rate with the purifier running, n is the natural particle decay rate in the chamber (infiltration and settling), and V is the chamber volume (1,008 cu ft).
Important caveat: CADR is always tested at the unit's maximum fan speed. Real-world performance at a quiet overnight setting is lower — often significantly so. The published score is a ceiling, not a constant.
CADR vs. CFM vs. ACH: Understanding the Difference
These three terms are often used interchangeably by retailers, but they measure different things:
- CADR (in CFM): How much clean air the purifier produces per minute. A property of the purifier, not the room.
- CFM (Cubic Feet per Minute): The airflow unit. Fan specs list raw CFM; CADR is "clean" CFM after filter efficiency is factored in.
- ACH (Air Changes per Hour): How many times per hour a purifier can cycle all the air in your specific room. This is a property of the purifier and the room together.
The ACH formula:
ACH = (CADR × 60) ÷ Room Cubic Feet
Room cubic feet = room square footage × ceiling height. For a standard 8-foot ceiling, a 300 sq ft room is 2,400 cubic feet.
Example: Levoit Core 400S at 231 CFM smoke CADR (AHAM Verifide) in a 300 sq ft room with 8-foot ceilings (2,400 cu ft):
ACH = (231 × 60) ÷ 2,400 = 5.8 ACH
That is 5.8 full air changes per hour at max fan speed — comfortably above the 4–5 ACH target for standard use.
How to Use CADR to Size a Purifier for Any Room
AHAM's published sizing guideline: a purifier's smoke CADR should equal at least two-thirds of the room's square footage. A 300 sq ft room needs 200+ CFM smoke CADR. A 500 sq ft room needs 333+ CFM.
The two-thirds rule is a minimum. For these scenarios, size up:
- Wildfire smoke or heavy pollution: Target smoke CADR equal to the room's full square footage (roughly 1.5× the standard guideline). A 300 sq ft room: 300+ CFM smoke CADR.
- Allergy sufferers: Target 6 ACH minimum. For a 300 sq ft room at 8-foot ceilings (2,400 cu ft), you need a CADR of at least 240 CFM.
- Open floor plans: Calculate total cubic feet including adjacent open areas. A kitchen open to a 400 sq ft living room is effectively 600–700 sq ft of shared airspace.
Room Size to CADR Quick Reference
All figures assume 8-foot ceilings. For taller ceilings, use the CADR calculator to compute ACH with your actual room volume.
| Room Size | Min Smoke CADR (Standard) | Smoke CADR for Smoke/Allergy | Suggested Model |
|---|---|---|---|
| Up to 200 sq ft (bedroom) | 133 CFM | 200 CFM | Coway AP-1512HH (233 CFM smoke, AHAM Verifide) |
| 200–350 sq ft (large bedroom / small living room) | 133–233 CFM | 200–350 CFM | Levoit Core 400S (231 CFM) or Winix 5500-2 (232 CFM) |
| 350–500 sq ft (living room) | 233–333 CFM | 350–500 CFM | Levoit Core 600S (391 CFM smoke, ENERGY STAR listed) |
| 500–700 sq ft (large open plan) | 333–467 CFM | 500–700 CFM | Levoit Core 600S — or two mid-range units |
| 700+ sq ft | 467+ CFM | 700+ CFM | Two units or a commercial-grade purifier |
CADR Ratings for Popular Models: ACH Calculations
Here is how CADR math plays out for four models across common room sizes. All calculations use smoke CADR, 8-foot ceilings, and max fan speed. Real-world ACH on lower fan speeds will be lower.
Coway AP-1512HH Mighty — 233 CFM Smoke CADR (AHAM Verifide)
- 150 sq ft bedroom (1,200 cu ft): ACH = (233 × 60) ÷ 1,200 = 11.7 ACH — excellent; unit will run comfortably on low-to-medium speed
- 250 sq ft room (2,000 cu ft): ACH = (233 × 60) ÷ 2,000 = 7.0 ACH — strong for allergy use
- 361 sq ft AHAM-rated room (2,888 cu ft): ACH = (233 × 60) ÷ 2,888 = 4.8 ACH — at AHAM's recommended coverage
Noise: 24–53 dB · Max power: 77 W · Filter cost: ~$60/yr · CARB: not verified
Levoit Core 600S — 391 CFM Smoke CADR (ENERGY STAR listed, not AHAM Verifide)
- 200 sq ft bedroom (1,600 cu ft): ACH = (391 × 60) ÷ 1,600 = 14.7 ACH — extreme overkill; unit runs on low speed most of the time
- 400 sq ft living room (3,200 cu ft): ACH = (391 × 60) ÷ 3,200 = 7.3 ACH — excellent, above 6 ACH allergy target
- 606 sq ft rated coverage (4,848 cu ft): ACH = (391 × 60) ÷ 4,848 = 4.8 ACH — at AHAM's recommended minimum
Filter type: True HEPA stage + activated carbon (3-stage) · Noise: 26–55 dB
Levoit Core 400S — 231 CFM Smoke CADR (AHAM Verifide)
- 200 sq ft bedroom (1,600 cu ft): ACH = (231 × 60) ÷ 1,600 = 8.7 ACH — strong allergy/smoke performance
- 300 sq ft room (2,400 cu ft): ACH = (231 × 60) ÷ 2,400 = 5.8 ACH — above standard target, adequate for allergy use
- 358 sq ft AHAM-rated room (2,864 cu ft): ACH = (231 × 60) ÷ 2,864 = 4.8 ACH — at the recommended minimum
Noise: 24–52 dB · Dust CADR: 240 CFM · Pollen CADR: 259 CFM
Winix 5500-2 — 232 CFM Smoke CADR (AHAM Verifide, CARB certified)
- 200 sq ft bedroom (1,600 cu ft): ACH = (232 × 60) ÷ 1,600 = 8.7 ACH — strong performance; washable AOC carbon filter keeps long-term costs low
- 300 sq ft room (2,400 cu ft): ACH = (232 × 60) ÷ 2,400 = 5.8 ACH — solid for allergy use
- 360 sq ft AHAM-rated room (2,880 cu ft): ACH = (232 × 60) ÷ 2,880 = 4.8 ACH — at spec; comfortable for standard use
Noise: 27.8–50 dB · Max power: 70 W · Includes PlasmaWave ionizer (disableable)
Common CADR Misconceptions
Misconception 1: The Rated Coverage Area Is the Whole Story
Manufacturer room-size claims may use different air-change assumptions. Some use AHAM's 4.8 ACH guideline; others use 2 ACH or even 1 ACH, which inflates the square footage from the same CADR. Example: the Coway AP-1512HH at 233 CFM smoke CADR is AHAM-rated for 361 sq ft (4.8 ACH), but Coway's own marketing claims 1,748 sq ft at a 1 ACH basis. Always check the stated ACH basis — or calculate ACH yourself from smoke CADR and your actual room volume.
Misconception 2: A Higher CADR Is Always Better
Oversizing wastes money on hardware. A highly oversized purifier will spend most of its time on low-speed settings to avoid noise, and its actual operating CADR at low speed is well below the published maximum. Match CADR to room size; about 1.5× oversizing is useful as a smoke/allergy buffer, beyond that is diminishing returns.
Misconception 3: CADR Tells You About VOC and Odor Removal
It does not. AHAM's CADR test covers particles only — smoke, dust, pollen. It says nothing about activated carbon performance, ozone output, or ability to remove VOCs, odors, formaldehyde, or gases. For VOC and odor removal, look at the carbon bed weight and type in the specs (ideally 1+ lb of granular activated carbon) and any independent VOC test data the manufacturer publishes.
Misconception 4: CADR Stays Constant as Filters Age
CADR is tested with a new, clean filter. As the HEPA media loads with captured particles, airflow restriction increases and effective CADR decreases. Replace filters on the manufacturer's recommended schedule — typically every 6–12 months depending on usage and air quality conditions.
Misconception 5: All CADR Claims Are Independently Verified
No. AHAM Verifide certification means the score was independently tested in an accredited lab. Many brands — particularly budget imports — publish self-reported CADR numbers with no third-party verification. ENERGY STAR product listings also publish CADR data, sourced from the manufacturer's application to the program. When comparing models, always note whether the CADR figure is AHAM Verifide, ENERGY STAR listed, or manufacturer-stated.
Wildfire Smoke CADR: The 1.5× Rule
The standard AHAM sizing guideline (smoke CADR = ⅔ of room sq footage) was developed for everyday household dust and allergens with 8-foot ceilings. Wildfire smoke is different: PM2.5 concentrations during active smoke events can spike to many times the EPA's "unhealthy" threshold indoors. The purifier needs to cycle air faster to keep indoor concentration at safer levels.
The 1.5× rule: for wildfire smoke or heavy pollution events, target a smoke CADR at least equal to your room's full square footage (rather than two-thirds). A 300 sq ft room: target 300+ CFM smoke CADR. At that CADR in a room with 8-foot ceilings, the purifier runs about 7.5 ACH — well above the standard 4.8 ACH minimum.
For more detail on purifier performance during smoke events, see our full guide to the best air purifiers for wildfire smoke.
Buyer's Guide: How to Choose by CADR
Step 1: Measure your room. Length × width = square footage. Multiply by ceiling height (standard: 8 ft; measure if vaulted or non-standard) for cubic footage.
Step 2: Set your ACH target. Standard household use: 4–5 ACH. Allergy sufferers: 6 ACH minimum. Wildfire smoke: 6+ ACH, or use the 1.5× square footage rule for smoke CADR directly.
Step 3: Calculate required CADR.
Required CADR = (Target ACH × Room Cubic Feet) ÷ 60
Or skip the math and use our CADR / room size calculator.
Step 4: Compare smoke CADR across models. Look for AHAM Verifide scores first. Do not compare smoke CADR from one unit against pollen CADR from another — always compare the same particle class.
Step 5: Check filter costs. A unit that fits your CADR needs but requires expensive filter replacements every 6 months has a high total cost of ownership. For a full breakdown, see our air purifier filter replacement cost guide.
Step 6: Reality-check the noise floor. CADR is measured at max fan speed. At sleep or low speed, the actual clean air delivery is well below the published number. Check the decibel rating at low speed — for bedroom use, look for units under 30 dB at low speed.
CADR FAQ
What does CADR stand for in air purifiers?
CADR stands for Clean Air Delivery Rate. It measures how much filtered air an air purifier delivers per minute, in cubic feet per minute (CFM). AHAM developed and administers the standard; independent labs conduct the testing. CADR is reported separately for three particle classes: smoke, dust, and pollen.
What CADR do I need for a 300 sq ft room?
Using AHAM's two-thirds rule (which assumes 8-foot ceilings), a 300 sq ft room needs a smoke CADR of at least 200 CFM. For wildfire smoke or heavy pollution, target a smoke CADR closer to the room's full square footage — 300 CFM — for faster air turnover. The Levoit Core 400S (231 CFM smoke CADR, AHAM Verifide) covers a 300 sq ft room at about 5.8 ACH on max speed.
Is a higher CADR always better?
Not necessarily. A high-CADR purifier in a small room cycles air more times per hour than needed. You will likely run it on a low fan speed, where actual CADR is well below the published maximum. Match CADR to room size: oversizing by about 1.5× provides a useful buffer for smoke events, but 3–4× oversizing wastes money on hardware without meaningful air quality improvement.
What is the difference between CADR, CFM, and ACH?
CADR (Clean Air Delivery Rate) measures how much clean air a purifier produces per minute in CFM (cubic feet per minute). CFM is the airflow unit. ACH (Air Changes per Hour) is how many times per hour a purifier can cycle all the air in a specific room — it combines the purifier's CADR with your room's cubic volume. ACH = (CADR × 60) ÷ room cubic feet.
Why does CADR have three separate scores (smoke, dust, pollen)?
Because different particle sizes behave differently. Smoke particles (0.09–1.0 microns) are the smallest and hardest to trap, so smoke CADR is usually the lowest of the three scores. Dust (0.5–3 microns) and pollen (5–11 microns) are larger and easier to filter. Use smoke CADR as your sizing benchmark for worst-case performance.
Do air purifiers lose CADR over time as filters age?
Yes. As a HEPA filter loads with captured particles, airflow restriction increases and effective CADR drops. Replacing filters on the manufacturer's recommended schedule — typically every 6–12 months depending on usage — keeps CADR close to the rated specification.
Does CADR measure gas or odor removal?
No. CADR only measures particle removal (smoke, dust, pollen). It does not reflect a purifier's ability to remove gases, VOCs, or odors. For gas-phase filtration, look at the activated carbon bed weight and type separately — CADR will not help you compare odor removal performance.
The Verdict: Match CADR to Your Room, Not the Box
CADR is a standardized benchmark — the closest thing air purifier shopping has to a reliable spec. Use it. Ignore the "covers up to X sq ft" claim on the box (check the ACH basis first) and calculate ACH yourself from the smoke CADR and your room's actual cubic footage. Target 4–5 ACH for standard use, 6+ for allergies or smoke events.
For most bedrooms under 250 sq ft, the Coway AP-1512HH Mighty (233 CFM smoke CADR, AHAM Verifide) hits the target at a competitive price. For medium rooms up to 350 sq ft, the Levoit Core 400S (231 CFM, AHAM Verifide) and Winix 5500-2 (232 CFM, AHAM Verifide, CARB certified) are strong options. For large rooms or smoke headroom, the Levoit Core 600S at 391 CFM (ENERGY STAR listed) is the clear choice.
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