What does CADR mean on an air purifier?

Clean Air Delivery Rate — the volume of genuinely particle-free air a purifier delivers, measured in cubic feet per minute. It combines two things that marketing usually separates: how much air the fan moves and how much of the particulate the filter actually removes. A powerful fan with a mediocre filter and a superb filter behind a weak fan both score poorly, which is exactly why the metric is useful. Certified figures come from AHAM's independent testing program, and a unit carrying the AHAM Verifide seal has had its numbers verified rather than self-reported.

What is a good CADR number?

It depends entirely on your room, which is the point of the metric. AHAM's two-thirds rule is the quick version: a purifier's smoke CADR should be at least two-thirds of the room's floor area in square feet, so a 300 square foot room wants a smoke CADR of at least 200. That guideline assumes 8-foot ceilings and delivers about 4.8 air changes per hour. For allergies, smoke or pets, size above the rule rather than to it, so you can run a larger unit on a quieter middle speed.

Why does a purifier have three CADR numbers?

Because particle size changes how easily a filter catches it, so AHAM tests three: smoke (0.09 to 1.0 microns), dust (0.5 to 3 microns) and pollen (5 to 11 microns). Smoke is the hardest test and always produces the lowest number, so it is the most conservative figure and the one to size by. Pollen is the easiest and always the highest, which is why marketing quotes it. If a listing shows only one large CADR number with no category named, assume it is pollen.

Is CADR the same as square footage coverage?

No, and the gap is where most disappointment comes from. Manufacturer coverage claims are typically calculated at only two air changes per hour, which is enough to make the box look impressive and not enough to control allergens or smoke. The same machine that claims 1,500 square feet at two air changes covers about 600 square feet at five. Ignore the coverage headline, find the CADR, and do the air-change math yourself — the numbers on the box and the numbers you need are answering different questions.

Does a HEPA filter guarantee a high CADR?

No. HEPA describes the filter's capture efficiency at a single particle size; CADR describes the whole machine's output. A true HEPA filter in a unit with a weak fan, a leaky housing that lets air bypass the filter, or a restrictive filter that chokes airflow can produce a low CADR despite the filter's rating. That is why AHAM's certified figure is worth more than a filter specification — it measures what comes out of the machine rather than what the medium can do in isolation.

Understanding CADR Ratings

Written & researched by Derek Holt Home & Appliances Editor

Updated October 2026

Three-quarter view of a person adjusting a floor-standing air purifier in a quiet living room, in soft early-morning light

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CADR stands for Clean Air Delivery Rate: the cubic feet per minute of genuinely particle-free air a purifier produces. It is the single most useful number on an air purifier because it combines fan output and filter efficiency into one figure that you can compare across brands. AHAM, the trade association that runs the independent test program, publishes three values — smoke, dust and pollen — and gives a quick sizing rule: the smoke CADR should be at least two-thirds of the room's floor area in square feet. A 300 square foot room therefore wants a smoke CADR of 200 or better. Everything else on the box is marketing.

We do not physically handle the products we rank; our picks come from aggregated owner reviews, published specifications and expert consensus — see how we rank.

Why there are three numbers

Filters do not treat all particles equally, so AHAM tests three size ranges and reports each separately:

CADR category	Particle size tested	Difficulty	Typical relative value
Smoke	0.09 – 1.0 microns	Hardest	Lowest of the three
Dust	0.5 – 3.0 microns	Moderate	Middle
Pollen	5 – 11 microns	Easiest	Highest of the three

Because smoke is the hardest test, it is the most conservative number and the one worth sizing by — a purifier that handles fine smoke particulate well handles everything larger comfortably. Pollen is the flattering figure, which is why a product listing showing a single large unattributed CADR is almost always quoting pollen. On most well-designed units the three numbers cluster within about 20 percent of each other; a wide spread suggests the filter struggles with fine particles.

One caution: CADR is a particulate metric only. It says nothing about odors, gases or VOCs, which are handled by the activated carbon stage and are not measured by this program at all. A purifier with an excellent CADR and a token carbon mesh will clear a smoky haze while leaving the smell exactly where it was.

Wide view of a person adjusting a floor-standing air purifier in a quiet living room, in soft early-morning light

Sizing it: the two-thirds rule and the better version

AHAM's rule of thumb is deliberately simple: smoke CADR ≥ room square footage × 2/3, assuming 8-foot ceilings. It works out to roughly 4.8 air changes per hour, which is a sensible target for a general-purpose purifier.

Room size	Minimum smoke CADR (two-thirds rule)	Recommended for allergies, pets or smoke
100 sq ft (small bedroom, office)	67	90 – 120
150 sq ft	100	130 – 170
200 sq ft (standard bedroom)	133	170 – 220
300 sq ft (large bedroom, den)	200	250 – 320
450 sq ft (living room)	300	380 – 480
600 sq ft (open plan)	400	500 – 650

If your ceilings are higher than 8 feet, or the room opens into another space, do the volume math directly instead:

Floor area × ceiling height = room volume in cubic feet.
Volume × the air changes you want ÷ 60 = required CADR.

A 14 by 16 foot living room with 9-foot ceilings is 2,016 cubic feet. At five air changes per hour that is 2,016 × 5 ÷ 60 = 168 CFM, so look for a smoke CADR of at least 168. Aim for two air changes in a general-comfort room, four in a bedroom, and five or more where allergies, pets or smoke are the reason you are buying — the reasoning behind those targets is in do air purifiers help allergies.

Wide view of a person adjusting a floor-standing air purifier in a quiet living room, in warm late-afternoon light

Why box coverage claims are inflated

Manufacturer square-footage claims and CADR are not in conflict; they are answering different questions. Coverage headlines are typically calculated at two air changes per hour, the minimum at which a purifier can be said to serve a room. So a unit advertised at 1,500 square feet is claiming two air changes across that area, and at the five air changes an allergy sufferer actually wants, the same machine covers roughly 600 square feet. Both figures are technically true. Only one of them describes what you will experience.

The other inflation comes from testing at maximum fan speed. CADR is measured on the highest setting, which on many units is loud enough that owners never use it. This is the strongest argument for buying one size up: a larger purifier on speed two delivers the CADR you need at a noise level you will tolerate, whereas a right-sized unit only hits its rating on a setting you will turn down. Owner reviews reflect this consistently — noise on high is among the most frequent complaints across the category.

Low-angle view of a person adjusting a floor-standing air purifier in a quiet living room, in warm evening lamplight

What CADR does not tell you

Nothing about odors or gases. Particulate only. Judge carbon by the weight of carbon in the filter, not by the CADR.
Nothing about noise or power draw at that output. Two units with identical CADR can differ substantially in decibels and watts. Running costs are broken down in air purifier running costs.
Nothing about filter cost. The cheapest route to a high CADR is sometimes an expensive consumable, so check the replacement filter price and interval — see how often to change a HEPA filter.
Nothing about your actual room. The test chamber is sealed. An open doorway, a running ceiling fan, or a purifier tucked behind furniture all reduce real-world performance below the rating — placement is covered in where to put an air purifier.
Nothing about long-term output. CADR is measured with a clean filter. A loaded filter delivers less, which is the quiet reason a purifier that used to work stops working.

Also note that not every manufacturer participates in AHAM's program. An absent CADR is not proof of a bad machine, but a self-reported figure with no independent verification carries less weight than a certified one, and some very large claimed coverage numbers belong to units with no third-party testing behind them at all.

Where to go next

With a target CADR in hand, compare models in best air purifiers, or go straight to the situation-specific picks: bedrooms, allergies, and wildfire smoke. Check the filter standard too, since CADR assumes the filter in the box — see true HEPA vs HEPA-type. All under the air quality hub.