CADR Explained Simply

CADR is the single most useful number when comparing air purifiers — yet most buyers ignore it. Here is what it means, why it matters, and how to use it correctly.

What CADR Measures

CADR stands for Clean Air Delivery Rate. It measures how quickly an air purifier delivers clean, filtered air into a room, expressed in cubic feet per minute (CFM) or cubic metres per hour (m³/h).

It was developed by the Association of Home Appliance Manufacturers (AHAM) and is tested in a standardised 1,008 ft³ (28.5 m³) chamber. Because every manufacturer uses the same test conditions, CADR scores are directly comparable across brands — unlike most other air purifier marketing claims.

CADR combines two factors: how much air passes through the purifier per minute, and how efficiently the filter removes particles from that air. A unit with high airflow but a weak filter can score similarly to a unit with moderate airflow but exceptional filtration — CADR captures the net result.

The Three CADR Scores

AHAM tests with three particle types, each representing a different size range:

Score	Particle type tested	Typical size	Real-world relevance
Smoke CADR	Tobacco smoke	0.1–1 µm	Wildfire smoke, PM2.5, fine particles
Dust CADR	Standard dust	0.5–3 µm	Household dust, pet dander, skin cells
Pollen CADR	Pollen-sized	5–11 µm	Seasonal allergies, large airborne particles

A well-designed air purifier should score comparably across all three. A unit with very high pollen CADR but low smoke CADR handles large particles well but may struggle with fine particulate — relevant if you live in a wildfire-risk area or near heavy traffic pollution.

Which score matters most for you:

General use or dust allergies → Dust CADR
Seasonal hay fever or pollen → Pollen CADR
Wildfire smoke, PM2.5, or cigarette smoke → Smoke CADR
Asthma or respiratory concerns → use Smoke CADR as the strictest benchmark

Matching CADR to Your Room Size

AHAM's published rule: your purifier's CADR should equal at least ⅔ of your room's square footage (at standard 8 ft / 2.4 m ceiling height). This delivers approximately 5 air changes per hour — the level associated with meaningful allergy and air quality benefit.

Formula: Minimum CADR (CFM) = Room square footage ÷ 1.5

Room size	Minimum CADR	Recommended CADR (allergy / asthma)
100 sq ft (small bedroom)	67 CFM	100+ CFM
150 sq ft (bedroom)	100 CFM	150+ CFM
200 sq ft (master bedroom)	133 CFM	180+ CFM
300 sq ft (large bedroom / studio)	200 CFM	260+ CFM
400 sq ft (living room)	267 CFM	330+ CFM
600 sq ft (open plan)	400 CFM	480+ CFM
1,000 sq ft	667 CFM	800+ CFM

Critical point: These figures assume the purifier runs at maximum speed. At medium speed, effective CADR typically drops 40–55%. At low/sleep speed, 60–70%. If you plan to use the unit in a bedroom at night on low mode, you need a significantly higher rated CADR than the room coverage figure suggests. A unit rated for 500 sq ft running at low speed may effectively cover only 200 sq ft.

CADR and Air Changes Per Hour (ACH)

Air changes per hour (ACH) measures how many complete room air cycles the purifier delivers each hour. More ACH = cleaner air, faster recovery after a pollution event.

ACH formula: (CADR in CFM × 60) ÷ Room volume in cubic feet

Example: CADR 250 CFM in a 300 sq ft room with 8 ft ceilings (2,400 ft³):

(250 × 60) ÷ 2,400 = 6.25 ACH

Target ACH levels:

2 ACH — minimum for general air quality improvement
4–5 ACH — recommended for allergy relief
5–6 ACH — recommended for asthma, smoke exposure, or respiratory conditions
6+ ACH — hospital isolation room standard

For a full explanation of ACH calculations and how room geometry affects them, see our ACH explained guide.

Real-World CADR vs Box Claims

Air purifier packaging often states room coverage in square feet — "covers up to 500 sq ft." This claim is based on just 2 air changes per hour, which is the minimum threshold for any air quality benefit. It is not a meaningful benchmark for allergy sufferers or anyone with air quality concerns.

Practical rule: halve the manufacturer's room coverage claim to get a figure that gives you 4–5 ACH. A unit marketed as covering 500 sq ft will deliver useful allergy-level filtration in roughly a 250 sq ft room.

CADR Comparison: Our Ranked Models

Model	Smoke CADR	Dust CADR	Pollen CADR	Effective room (5 ACH)
Levoit Core 600S	410 CFM	423 CFM	445 CFM	~500 sq ft
Blueair Blue Pure 211i Max	350 CFM	380 CFM	430 CFM	~425 sq ft
Coway AP-1512HH Mighty	246 CFM	240 CFM	240 CFM	~295 sq ft
Winix 5500-2	232 CFM	243 CFM	246 CFM	~280 sq ft
Dyson Purifier Cool TP07	~192 CFM	~196 CFM	~204 CFM	~230 sq ft
Levoit Core 300	145 CFM	140 CFM	141 CFM	~175 sq ft

See the full side-by-side comparison including noise levels, filter costs, and smart features for all six models.

How to Use CADR When Shopping

CADR figures are usually buried in the product spec sheet rather than the main listing. Here is a reliable shopping process:

Measure your room — length × width in feet. Multiply by ceiling height if non-standard (over 9 ft).
Calculate minimum CADR — room sq ft ÷ 1.5 = minimum smoke CADR at full speed.
Account for your actual fan speed — if you'll run it on medium in the bedroom, multiply your minimum CADR by 1.8× to get the headline CADR you need.
Cross-reference the AHAM directory — ahamdir.com lists certified purifiers with verified CADR scores. If a product is not listed, CADR is self-reported and unverified.
Check all three scores — a unit with high pollen CADR but low smoke CADR has a filter that handles large particles well but may struggle with fine PM2.5. For smoke and wildfire concerns, smoke CADR is the critical figure.

Quick check: divide the manufacturer's maximum room coverage claim by 2.5. That gives you an approximate effective room size at 5 ACH (the useful allergy-level benchmark). A unit "covering 600 sq ft" effectively handles 240 sq ft at 5 ACH.

CADR Limitations

CADR is the most useful single metric, but it has real constraints:

Maximum speed only — CADR is tested at full power. Actual performance at medium or low speed is substantially lower and not standardised.
No VOC or gas measurement — carbon filter effectiveness has no CADR equivalent. Manufacturers self-report odour removal performance.
AHAM certification is voluntary — some reputable brands (Blueair, Dyson) self-report CADR figures without AHAM certification. Others don't publish CADR at all — treat the absence of CADR data as a caution flag.
Tested in a sealed chamber — real rooms have air leaks, furniture obstructions, and varying door states that reduce effective filtration.

FAQ

What is a good CADR for a bedroom?

For a typical 150–200 sq ft bedroom, aim for a smoke CADR of 150–200 CFM to get 4–5 ACH at medium speed. For allergy or asthma sufferers who will run the unit on low/sleep mode overnight, choose a model with 200–250+ CFM so effective low-speed CADR still covers the room adequately. The Coway AP-1512HH at 246 CFM and the Winix 5500-2 at 232 CFM are well-suited to bedroom use.

Why does the box say "covers 500 sq ft" when CADR says less?

Manufacturers base room coverage claims on 2 air changes per hour — the lowest threshold for any air quality benefit. AHAM's ⅔ rule delivers 5 ACH, which is what you need for meaningful allergy or smoke benefit. Always calculate from the CADR figure using the formula above, not from the marketing coverage claim.

Is higher CADR always better?

Within your room size requirement, yes. Beyond that point, additional CADR doesn't help — you're already cycling the air more than necessary. The tradeoffs at higher CADR are typically higher noise (a larger or faster fan is needed), higher price, and larger unit size. Match CADR to your room, don't over-specify.

Does CADR apply to robot vacuum or other appliances?

No. CADR is specific to air purifiers and is measured by AHAM under the AC-1 standard. It has no equivalent in other appliance categories. Some air conditioning and HVAC systems publish airflow figures in CFM, but these are not comparable to air purifier CADR.

Related guides and rankings

Our ranked models: Levoit Core 600S · Coway AP-1512HH · Winix 5500-2 · Blueair Blue Pure 211i Max · Levoit Core 300 · Dyson TP07