CADR by room size

Researched from the AHAM AC-1 test method, EPA and CARB guidance, and published manufacturer specifications

Quick answer

Required CADR equals floor area times ceiling height times air changes an hour, divided by sixty. At an eight foot ceiling that puts a 300 square foot room at 180 CFM for four and a half air changes an hour and 80 CFM for two. There are 30 room sizes worked out in full here.

AHAM's two thirds convention is the same arithmetic with an eight foot ceiling and five air changes an hour already filled in, because 8 x 5 / 60 = 0.667.

Required clean air delivery rate by room size, eight foot ceiling
Room sizeVolumeAt 2 ACHAt 4.5 ACHAt 6 ACHTwo thirds rule
60 sq ft 480 cu ft 16 CFM 36 CFM 48 CFM 40 CFM
80 sq ft 640 cu ft 21 CFM 48 CFM 64 CFM 53 CFM
100 sq ft 800 cu ft 27 CFM 60 CFM 80 CFM 67 CFM
120 sq ft 960 cu ft 32 CFM 72 CFM 96 CFM 80 CFM
140 sq ft 1,120 cu ft 37 CFM 84 CFM 112 CFM 93 CFM
150 sq ft 1,200 cu ft 40 CFM 90 CFM 120 CFM 100 CFM
175 sq ft 1,400 cu ft 47 CFM 105 CFM 140 CFM 117 CFM
200 sq ft 1,600 cu ft 53 CFM 120 CFM 160 CFM 133 CFM
225 sq ft 1,800 cu ft 60 CFM 135 CFM 180 CFM 150 CFM
250 sq ft 2,000 cu ft 67 CFM 150 CFM 200 CFM 167 CFM
275 sq ft 2,200 cu ft 73 CFM 165 CFM 220 CFM 183 CFM
300 sq ft 2,400 cu ft 80 CFM 180 CFM 240 CFM 200 CFM
325 sq ft 2,600 cu ft 87 CFM 195 CFM 260 CFM 217 CFM
350 sq ft 2,800 cu ft 93 CFM 210 CFM 280 CFM 233 CFM
400 sq ft 3,200 cu ft 107 CFM 240 CFM 320 CFM 267 CFM
450 sq ft 3,600 cu ft 120 CFM 270 CFM 360 CFM 300 CFM
500 sq ft 4,000 cu ft 133 CFM 300 CFM 400 CFM 333 CFM
550 sq ft 4,400 cu ft 147 CFM 330 CFM 440 CFM 367 CFM
600 sq ft 4,800 cu ft 160 CFM 360 CFM 480 CFM 400 CFM
650 sq ft 5,200 cu ft 173 CFM 390 CFM 520 CFM 433 CFM
700 sq ft 5,600 cu ft 187 CFM 420 CFM 560 CFM 467 CFM
750 sq ft 6,000 cu ft 200 CFM 450 CFM 600 CFM 500 CFM
800 sq ft 6,400 cu ft 213 CFM 480 CFM 640 CFM 533 CFM
900 sq ft 7,200 cu ft 240 CFM 540 CFM 720 CFM 600 CFM
1000 sq ft 8,000 cu ft 267 CFM 600 CFM 800 CFM 667 CFM
1100 sq ft 8,800 cu ft 293 CFM 660 CFM 880 CFM 733 CFM
1200 sq ft 9,600 cu ft 320 CFM 720 CFM 960 CFM 800 CFM
1400 sq ft 11,200 cu ft 373 CFM 840 CFM 1120 CFM 933 CFM
1500 sq ft 12,000 cu ft 400 CFM 900 CFM 1200 CFM 1000 CFM
2000 sq ft 16,000 cu ft 533 CFM 1200 CFM 1600 CFM 1333 CFM
A machine for the middle of this table

MOOKA Air Purifier for Home Bedroom Large Room 2200 Ft2, HEPA Filter, Black

Enough airflow for a typical living room at four and a half air changes an hour, with a published specification that can be checked against the requirement rather than a coverage claim with no rate behind it.

$84.18Check pricePrices change often

Prices and specifications change, so check the listing against the figure your own room needs.

How to use this table

Find your floor area, read across to the air change rate you want, and that is the clean air delivery rate a machine has to publish. Then compare it against a machine's smoke CADR, which is the lowest and most conservative of the three figures the AHAM test produces.

If your ceiling is not eight feet, the individual pages work the same room at seven, nine, ten and twelve feet. It matters more than people expect: the same floor area at ten feet needs a quarter more airflow for the same result.

Machines with a published airflow figure

Common questions

What is CADR?

Clean air delivery rate, in cubic feet per minute, measured under the ANSI/AHAM AC-1 test method in a sealed 1,008 cubic foot chamber. It is how much genuinely filtered air a machine delivers rather than how much air its fan moves, and it is measured separately for smoke, dust and pollen, so each machine carries three numbers.

How many air changes an hour should I aim for?

Two is the general comfort case. Four to five is the figure usually given where somebody in the household reacts to pollen, dander or dust, and it is guidance rather than a measured threshold. Six or more is where smoke guidance sits, because smoke keeps arriving while the machine is removing it.

Does the two thirds rule work?

It works for an eight foot ceiling and five air changes an hour, because that is what it assumes. A room with a ten foot ceiling needs a quarter more airflow than the rule suggests, and a household happy with two air changes an hour needs less than half of it. Knowing what it assumes is what makes it useful.

Should I use the smoke CADR or the dust one?

The smoke figure. It is measured against the smallest particle size in the test and is usually the lowest of the three, so sizing against it is the conservative choice. A single headline CADR with no particle size named is normally the highest of the three numbers.

What if my room is bigger than anything listed?

Two machines, placed apart, will serve a large room better than one in a corner, because a single unit recirculates its own clean air. The calculator refuses rather than recommending a machine that cannot deliver the rate asked for, and tells you the airflow each of two units would need.

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