The CADR formula
The calculation is CADR in CFM = room area in square feet × ceiling height in feet × target ACH ÷ 60. It estimates the clean-air delivery rate needed to cycle the room volume at the target rate.
Enter the room you want to clean, not the whole home. An open-plan space may need a larger measured area, while a closed bedroom needs only that room’s dimensions. The result is a comparison input, so use a published CADR from the exact purifier model.
Why the default is 4.8 ACH
Our air-purifier comparisons use 4.8 air changes an hour as a consistent assumption. It helps put published CADR figures on the same room-size basis. You can change the target rate in the calculator when your comparison needs a different assumption.
The default is not a safety standard, a guarantee of particle reduction or a recommendation for every room. Placement, doors, outdoor air, sources of pollution and the filter’s condition can change real results. Our air methodology explains the other factors we compare.
What CADR does not answer
CADR does not show whether a purifier provides fresh-air ventilation. It also does not guarantee removal of gases, odors or every pollutant. Check the exact model’s published filter details and use the product for the scope its documentation supports.
Compare the calculated requirement with the published CADR, then consider noise, replacement-filter cost, ionizer settings, placement and warranty. See our medium-room comparison for an example of a like-for-like comparison.
Calculate and compare
| Product / model | CADR as recorded | Room-size claim and assumptions | Sources |
|---|---|---|---|
| Alen BreatheSmart 45i US BreatheSmart 45i | No CADR value recorded. Airflow is not substituted for CADR. | 950 sq ft at 2 air changes an hour or 1,900 sq ft at 1, by Alen's figures. Its FAQ says up to 1,600 sq ft. | Alen: BreatheSmart 45i official US product page (manufacturer, checked Oct 13, 2026) Alen: Product and Warranty Information (manufacturer, checked Oct 13, 2026) |
| Austin Air HealthMate HealthMate standard model | Not published by Austin Air | Not published. Austin Air says only that it can clean large rooms | Austin Air: HealthMate (manufacturer, checked Oct 13, 2026) Austin Air: HealthMate (Austin Air online store) (manufacturer, checked Oct 13, 2026) |
| Blueair Blue Pure 311i Max US model; particle and carbon filter included | 283, 314 and 365 cfm | 439 ft² at 4.8 air changes an hour (one change every 12.5 minutes) | Blueair: Blue Pure 311i Max (manufacturer, checked Oct 13, 2026) US EPA ENERGY STAR: ENERGY STAR Certified Room Air Cleaners: Blueair 3332111100 (certifier, checked Oct 13, 2026) |
| Blueair Blue Pure 511 US model, store item 109994, with one Particle + Carbon filter and an Arctic Trail pre-filter | 122, 123 and 123 cfm | 189 ft² at 4.8 air changes an hour (one change every 12.5 minutes) | Blueair: Blue Pure 511 (manufacturer, checked Oct 13, 2026) |
| Coway Airmega AP-1512HH Mighty US AP-1512HH / AP-1512HH(W) | 233, 246 and 240 | 361 ft² at 4.8 air changes an hour (one change every 12.5 minutes); 874 ft² at 2; 1,748 ft² at 1 | Coway: Airmega Mighty AP-1512HH (manufacturer, checked Oct 13, 2026) Coway: Airmega Mighty AP-1512HH user manual (US) (manufacturer, checked Oct 13, 2026) |
| IQAir Atem Desk US Atem Desk | Not published by IQAir | IQAir says up to 150 ft², with no air-change rate. Even at 39 cfm, a 150 ft² room with 8 ft ceilings gets just under 2 air changes an hour | IQAir: Atem Desk technical specifications (manufacturer, checked Oct 13, 2026) IQAir: Atem Desk Air Purifier (manufacturer, checked Oct 13, 2026) |
| Levoit Core 300-P US Core 300-P | 143 CFM; Levoit gives one figure, not separate smoke, dust and pollen ratings | 222 ft² at 4.8 air changes an hour; 1,066 ft² at 1 | Levoit: Levoit Core® 300-P Black Air Purifier (manufacturer, checked Oct 13, 2026) Levoit: Levoit Core® 300-P Air Purifier (manufacturer, checked Oct 13, 2026) |
| Levoit Vital 200S-P Vital 200S-P, Black / LAP-V201S-WUS | 250 CFM; Levoit gives one figure, not separate smoke, dust and pollen ratings | 388 ft² at 4.8 air changes an hour; 1,862 ft² at 1 | Levoit: Levoit Vital 200S-P Smart Air Purifier (manufacturer, checked Oct 13, 2026) Levoit: Levoit Vital 200S-P Smart Air Purifier - Black (manufacturer, checked Oct 13, 2026) |
| Rabbit Air MinusA2 US MinusA2 | 180, 193 and 200; Rabbit Air doesn't name the test standard | Rabbit Air says 408 ft² at 4 air changes an hour or 815 ft² at 2 (8 ft ceiling, top speed). Those match its 218 CFM airflow. On the 180 smoke CADR, 4.8 air changes an hour fits about 280 ft². | Rabbit Air: MinusA2 Ultra Quiet Air Purifier (manufacturer, checked Oct 13, 2026) |
| Winix 5500-2 US 5510, the closest current model to the discontinued 5500-2 Successor figures: do not apply these to the legacy model. | 253, 252 and 247 | 392 ft² at 4.8 air changes an hour (8 ft ceilings). Winix also says it cleans 941 ft² in 30 minutes and 1,882 ft² in an hour | Winix: Winix 5510 - Air Purifier with WiFi & PlasmaWave® Technology (manufacturer, checked Oct 13, 2026) Winix: Winix 5520 - Air Purifier with WiFi & PlasmaWave® Technology (manufacturer, checked Oct 13, 2026) Winix: 5510 and 5520 user manual (manufacturer, checked Oct 13, 2026) |
Particle CADR does not establish gas removal, infection protection or a health outcome. No airflow figure is silently treated as CADR.
How this was written. Last updated . It is general information, not medical advice. Talk to a clinician before acting on anything here if you have a health condition or take medication.
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