CADR is the single most useful number on an air purifier's spec sheet -- and the most misunderstood. Manufacturers use it selectively, retailers rarely explain it, and buyers end up with purifiers that are either hopelessly undersized for their room or so oversized they run at earsplitting speeds to do a job a mid-range unit could handle quietly.
This guide explains exactly what CADR means, how AHAM tests and certifies it, why there are three separate scores, and -- most importantly -- how to use the number to match a purifier to your specific room before you spend a dollar. At the bottom, we apply the formula to four popular models across different room sizes so you can see the math in action.
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CADR Ratings for Popular Air Purifiers in 2026
Verified AHAM-tested or manufacturer-published CADR data. Smoke CADR is the conservative benchmark -- use it for sizing.
| Model | Smoke CADR | Dust CADR | Pollen CADR | Rated Coverage | Price |
|---|---|---|---|---|---|
| Levoit Core 600S | 391 CFM | 410 CFM | 423 CFM | 635 sq ft | Check Price on Amazon |
| Levoit Core 400S | 231 CFM | 243 CFM | 260 CFM | 403 sq ft | Check Price on Amazon |
| Coway AP-1512HH Mighty | 141 CFM | 200 CFM | 246 CFM | 360 sq ft | Check Price on Amazon |
| Winix 5500-2 | 232 CFM | 243 CFM | 246 CFM | 360 sq ft | Check Price on Amazon |
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 200 CFM -- because only half the outgoing air is actually clean. That distinction is why CADR is more useful than fan airflow specs.
The formula is: CADR = Airflow (CFM) x Filter Efficiency (%)
A purifier with 300 CFM fan airflow and 99.97% True HEPA efficiency (for 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
AHAM certifies three separate CADR scores for every tested unit, using tracer particles of different sizes:
- Smoke CADR -- uses potassium chloride particles in the 0.09-1.0 micron range. The hardest particles for filters to capture. Always 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 ragweed pollen in the 5-11 micron range. Large particles, easiest to filter. Always 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 are relatively close together. A "HEPA-type" filter at 85-90% efficiency struggles more with the smallest smoke particles, so the smoke score drops noticeably below pollen.
Use smoke CADR as your sizing benchmark. It represents worst-case filtration performance. If a purifier can clean your room adequately at smoke CADR, it will handle dust and pollen with headroom to spare.
How AHAM Tests CADR
AHAM testing is conducted in a sealed 1,008 cubic foot room (roughly 12x14 ft with 8 ft ceilings). The room 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 using the equation:
CADR = (k - n) x V
Where k is the particle decay rate with the purifier running, n is the natural particle decay rate in the room (infiltration/settling), and V is room volume in cubic feet.
Third-party labs run the tests and AHAM certifies the results. Look for the AHAM Verifide seal on the packaging or product listing -- it means the number was independently verified, not just manufacturer-claimed.
Important caveat: CADR is always tested at max fan speed. A purifier running on sleep or medium speed delivers significantly lower CADR. The published score is a ceiling, not a constant.
CADR vs CFM vs ACH: Understanding the Difference
These three terms get used interchangeably by retailers, but they measure different things:
- CADR (CFM): How much clean air the purifier produces per minute. A property of the purifier, not the room.
- CFM: 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 x 60) / Room Cubic Feet
Room cubic feet = Room sq footage x Ceiling height. For a standard 8 ft ceiling, a 300 sq ft room is 2,400 cubic feet.
Example: Levoit Core 400S at 231 CFM smoke CADR in a 300 sq ft room (2,400 cu ft):
ACH = (231 x 60) / 2,400 = 13,860 / 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 and the 6 ACH target for allergy sufferers.
How to Use CADR to Size a Purifier for Any Room
AHAM's published sizing rule: 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.
That is the minimum. For these scenarios, size up:
- Wildfire smoke or heavy pollution events: Apply the 1.5x rule. Target smoke CADR equal to the room's full square footage. A 300 sq ft room: 300+ CFM smoke CADR.
- Allergy sufferers: Target 6 ACH minimum. Back-calculate: for a 300 sq ft room at 8 ft ceilings (2,400 cu ft), you need CADR of at least 240 CFM (240 x 60 / 2,400 = 6.0 ACH).
- High-occupancy rooms: More people = more CO2, VOCs, and particles generated continuously. Size up 25-50%.
- 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
| Room Size | Min CADR (Standard) | CADR for Smoke/Allergy | Suggested Model |
|---|---|---|---|
| Up to 150 sq ft (bedroom) | 100 CFM | 150 CFM | Coway AP-1512HH (141 CFM) |
| 150-300 sq ft (large bedroom) | 100-200 CFM | 150-300 CFM | Coway AP-1512HH or Winix 5500-2 |
| 300-500 sq ft (living room) | 200-333 CFM | 300-500 CFM | Levoit Core 400S (231 CFM) or Core 600S |
| 500-700 sq ft (large open plan) | 333-467 CFM | 500-700 CFM | Levoit Core 600S (391 CFM) -- or two mid-range units |
| 700+ sq ft | 467+ CFM | 700+ CFM | Two Levoit Core 600S units or commercial-grade unit |
CADR Ratings for Popular Models: Four Real Calculations
Here is how CADR math plays out for four models across three common room sizes. All calculations use smoke CADR, 8 ft ceilings, and max fan speed.
Levoit Core 600S -- 391 CFM Smoke CADR
- 150 sq ft bedroom (1,200 cu ft): ACH = (391 x 60) / 1,200 = 19.6 ACH -- extreme overkill, unit will run on low speed most of the time
- 400 sq ft living room (3,200 cu ft): ACH = (391 x 60) / 3,200 = 7.3 ACH -- excellent, above 6 ACH allergy target
- 635 sq ft open plan (5,080 cu ft): ACH = (391 x 60) / 5,080 = 4.6 ACH -- at AHAM's minimum recommended coverage
Check current price for Levoit Core 600S on Amazon
Levoit Core 400S -- 231 CFM Smoke CADR
- 200 sq ft bedroom (1,600 cu ft): ACH = (231 x 60) / 1,600 = 8.7 ACH -- strong allergy/smoke performance for a typical master bedroom
- 300 sq ft room (2,400 cu ft): ACH = (231 x 60) / 2,400 = 5.8 ACH -- above standard target, adequate for allergy use
- 403 sq ft rated room (3,224 cu ft): ACH = (231 x 60) / 3,224 = 4.3 ACH -- borderline; fine for dust/pollen, light for smoke events
Check current price for Levoit Core 400S on Amazon
Coway AP-1512HH Mighty -- 141 CFM Smoke CADR
- 150 sq ft bedroom (1,200 cu ft): ACH = (141 x 60) / 1,200 = 7.1 ACH -- excellent for a standard bedroom at a budget price
- 250 sq ft room (2,000 cu ft): ACH = (141 x 60) / 2,000 = 4.2 ACH -- adequate for standard use, light for smoke
- 360 sq ft rated room (2,880 cu ft): ACH = (141 x 60) / 2,880 = 2.9 ACH -- below the recommended minimum; the Coway is sized for bedrooms, not large rooms
Check current price for Coway AP-1512HH on Amazon
Winix 5500-2 -- 232 CFM Smoke CADR
- 200 sq ft bedroom (1,600 cu ft): ACH = (232 x 60) / 1,600 = 8.7 ACH -- strong performance for a bedroom; washable carbon filter keeps long-term costs low
- 300 sq ft room (2,400 cu ft): ACH = (232 x 60) / 2,400 = 5.8 ACH -- solid for allergy use
- 360 sq ft rated room (2,880 cu ft): ACH = (232 x 60) / 2,880 = 4.8 ACH -- at spec; comfortable for standard use
Check current price for Winix 5500-2 on Amazon
Common CADR Misconceptions
Misconception 1: The Rated Coverage Area Is the Whole Story
Manufacturers' coverage area claims are based on their own formulas, not AHAM's. Some base it on 4 ACH (AHAM's minimum), some on 2 ACH, and some on a proprietary formula that results in inflated numbers. Always calculate ACH yourself from the smoke CADR and your actual room's cubic footage rather than trusting the "covers up to X sq ft" claim on the box.
Misconception 2: A Higher CADR Is Always Better
Oversizing wastes energy and money. More importantly, 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 may be no better than a correctly sized unit running on medium. Match CADR to room size; 1.5x oversizing is useful as a smoke/allergy buffer, 3x+ is diminishing returns.
Misconception 3: CADR Tells You About VOC and Odor Removal
It does not. AHAM's CADR test covers particles -- smoke, dust, pollen. It says nothing about a unit's activated carbon layer, ozone output, or ability to remove VOCs, odors, formaldehyde, or gases. A unit with a thin carbon-impregnated sheet will score identically to one with a deep granular carbon bed on the CADR test. For VOCs and odors, look for carbon bed weight in the specs (ideally 1+ lb of granular activated carbon) and independent VOC test data.
Misconception 4: CADR Stays Constant as Filters Age
CADR is tested with a new, clean filter. As the HEPA media loads up with captured particles, airflow restriction increases and effective CADR decreases. Running a purifier past its recommended filter replacement interval can reduce real-world CADR by 20-40%. Replace filters on schedule -- and during heavy wildfire smoke seasons, earlier than the manufacturer recommends.
Misconception 5: All CADR Claims Are Independently Verified
No. AHAM certification (the Verifide seal) means the score was independently tested. Many brands -- particularly budget imports on Amazon -- publish self-reported CADR numbers with no third-party verification. Those numbers can be significantly inflated. The Coway AP-1512HH, Levoit Core 400S, Levoit Core 600S, and Winix 5500-2 are all AHAM-certified. Always check for the Verifide seal before trusting a CADR claim.
Wildfire Smoke CADR: The 1.5x Rule Explained
The standard AHAM sizing rule (CADR = 2/3 of room sq footage) was developed for everyday household dust and allergens. Wildfire smoke is different: PM2.5 concentrations during active smoke events can hit 150-300 micrograms per cubic meter indoors -- 10-20x the EPA's "unhealthy" threshold. The purifier needs to cycle air faster to keep indoor concentration at safe levels.
The 1.5x 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 of it. A 300 sq ft room: target 300+ CFM smoke CADR.
At that CADR, the purifier is running about 7.5 ACH in the room -- sufficient to dramatically reduce PM2.5 concentration even when outdoor smoke is actively infiltrating through gaps. Studies by Lawrence Berkeley National Laboratory found that running a properly sized HEPA purifier during smoke events reduces indoor PM2.5 by 50-80% compared to no purifier, with the effect strongest in rooms where ACH exceeds 6.
For the best smoke performance, 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 x width = square footage. Multiply by ceiling height (usually 8 ft) for cubic footage.
Step 2: Set your ACH target. Standard household use: 4-5 ACH. Allergy sufferers: 6 ACH minimum. Wildfire smoke events: 6+ ACH, or use the 1.5x sq footage rule for smoke CADR directly.
Step 3: Calculate required CADR. Required CADR = (Target ACH x Room Cubic Feet) / 60
Step 4: Use smoke CADR to compare. Look up the manufacturer-published smoke CADR for any unit you are considering. Filter by AHAM-certified units first. Do not compare smoke CADR from one unit against pollen CADR from another.
Step 5: Check filter costs. A unit that is perfect on CADR but requires $120 filters every six 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. A high-CADR unit running at 20% fan speed to stay quiet in your bedroom is delivering far less than its rated CADR. Check the decibel rating at sleep or low speed, not just at max. 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 do the testing.
What CADR do I need for a 300 sq ft room?
For normal allergy and dust use, a 300 sq ft room needs roughly 200 CFM smoke CADR (two-thirds of room sq footage). For wildfire smoke or heavy odors, apply the 1.5x rule and target 300+ CFM -- which puts you at the Levoit Core 400S (231 CFM) or Core 600S (391 CFM) for extra headroom.
Is a higher CADR always better?
Not automatically. A high-CADR purifier in a small room cycles air more times per hour than needed and runs at unnecessarily high -- or more likely very low -- fan speeds. Match CADR to room size: 1.5x oversizing is useful as a smoke/allergy buffer, beyond that is diminishing returns and wasted spend.
What is the difference between CADR, CFM, and ACH?
CADR is how much clean air the purifier produces per minute. CFM is the airflow unit CADR is expressed in. ACH (Air Changes per Hour) is how many times per hour a purifier completely cycles the air in your specific room -- it combines the purifier's CADR with your room's cubic volume. ACH = (CADR x 60) / room cubic feet.
Why does CADR have three separate scores?
Because different particle sizes behave differently and are harder for filters to capture. Smoke particles (0.09-1.0 microns) are the smallest and hardest to trap -- smoke CADR is almost always the lowest score and the most conservative sizing benchmark. Dust and pollen are larger and easier to filter, so their CADR scores are higher.
Do air purifiers lose CADR over time as filters age?
Yes. As the HEPA filter loads with captured particles, airflow restriction increases and effective CADR drops. Running a purifier past its recommended filter replacement interval can reduce real-world CADR by 20-40%. Replace filters on schedule -- and during heavy smoke seasons, proactively before the indicator triggers.
Which air purifiers have the best CADR per dollar in 2026?
The Levoit Core 400S delivers 231 CFM smoke CADR at roughly $182 -- strong CADR-per-dollar for medium rooms. The Coway AP-1512HH Mighty at around $100-$130 is the value leader for smaller rooms (141 CFM smoke CADR). The Levoit Core 600S at $250 offers 391 CFM -- the best large-room value in the current mid-range market.
The 2026 Verdict: Match CADR to Your Room, Not the Box
CADR is a standardized, independently tested 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 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.
For most bedrooms under 200 sq ft, the Coway AP-1512HH Mighty hits the target at the lowest price. For medium rooms up to 400 sq ft, the Levoit Core 400S is the best CADR-per-dollar option in 2026. For large rooms or anyone who wants smoke headroom, the Levoit Core 600S at 391 CFM smoke CADR is the clear choice.
Related reading:
- Best Air Purifiers for Wildfire Smoke 2026
- Air Purifier Filter Replacement Costs: 5-Year Comparison
- Levoit Core 300S vs Core 400S: Which Model to Buy?
- Coway Airmega 400 vs Levoit Core 600S: Full Comparison
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