Air Purifier Room & CADR Calculator
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Determine the Clean Air Delivery Rate (CADR) your air purifier needs to effectively filter a given room. Based on the AHAM (Association of Home Appliance Manufacturers) standard formula used to certify air purifiers sold in the United States.
Room & Filtration Settings
Standard residential: 8 ft. Older homes: 7–7.5 ft. Modern/vaulted: 9–12 ft.
Required CADR: —
Room Volume: —
Floor Area: —
Recommended for rooms up to: —
ACH Recommendations by Need
| Condition / Use Case | Recommended ACH | Notes |
|---|---|---|
| General / Everyday | 2–3 | Minimum for basic air quality maintenance |
| Allergies (pollen, dust mites) | 4.8 | AHAM recommended minimum for allergy sufferers |
| Asthma | 6 | Higher turnover reduces airborne triggers |
| Wildfire Smoke | 6+ | EPA recommends highest feasible ACH during smoke events |
| Pet Dander / Odors | 4–5 | Depends on pet count and sensitivity |
| VOCs / Chemical Sensitivity | 5–6 | Requires activated carbon stage; CADR alone insufficient |
Common CADR to Room Size Reference
| CADR (CFM) | Room Size @ 4.8 ACH (sq ft) | Typical Purifier Class |
|---|---|---|
| 100 | 155 | Small bedroom / office |
| 200 | 310 | Large bedroom / living room |
| 300 | 465 | Open-plan area |
| 400+ | 620+ | Whole-floor / commercial |
How to Use This Calculator
The AHAM standard recommends sizing a purifier to deliver at least 4.8 air changes per hour for the target room. This means the entire volume of air in the room passes through the filter 4.8 times every hour. For a 15×12 ft bedroom with 8-foot ceilings (1,440 cubic feet), you need a CADR of at least 115 CFM at 4.8 ACH.
Note: CADR ratings on purifier packaging typically reflect the unit's performance on the highest fan speed. Real-world use at lower, quieter speeds will deliver proportionally less CADR — often 40–60% of the rated value.