Is It Worth It? Quick Verdict
What Are the Key Benefits?
Right-Sized Purification
A unit with too-low CADR for your room won't cycle air enough times per hour. Our calculator ensures you get 4-5 ACH minimum.
Avoid Overpaying
Don't buy a $900 unit for a small bedroom when a $150 unit will do. Our calculator prevents overspending on unnecessary capacity.
CADR Matching
We calculate the minimum CADR based on room volume and target ACH, so you can compare units apples-to-apples.
Multi-Room Planning
Calculate for each room separately — one large unit rarely beats one unit per room for actual air quality improvement.
What Is It and How Does It Work?
Choosing the right air purifier depends on your room size and the unit's CADR (Clean Air Delivery Rate). This calculator helps you find the right unit by matching your room's square footage and ceiling height to the minimum CADR needed for 4-5 air changes per hour — the ACH recommended for allergy and asthma relief.
✅ Pros
- Free, instant results
- Accounts for room volume and ACH
- Recommends specific models by room size
- Prevents the #1 mistake: undersized purifiers
❌ Cons
- Doesn't account for unusual room shapes or high ceilings (adjust manually)
- CADR ratings vary by manufacturer testing standards
- Actual ACH depends on room layout and airflow patterns
Room Size & Usage Guide
| Room Type / Use Case | Recommended Setup |
|---|---|
| Small room (under 200 sq ft, 8ft ceiling) | Minimum CADR: 100+. Best picks: Levoit Core 300S, Winix 5500-2, Coway Airmega 200M |
| Medium room (200-400 sq ft, 8-10ft ceiling) | Minimum CADR: 200+. Best picks: AirDoctor 3000, Blue Pure 211+, Coway Airmega 300 |
| Large room (400-700 sq ft, 8-10ft ceiling) | Minimum CADR: 350+. Best picks: AirDoctor 5500, IQAir HealthPro Plus, Coway Airmega 400 |
| Open floor plan (700+ sq ft) | Minimum CADR: 500+. Best picks: Austin Air HealthMate, IQAir GC MultiGas, or multiple units |
Where Can You Buy It?
Trusted brands we recommend based on CADR ratings, filter quality, and real-world performance.
Frequently Asked Questions
What is ACH and how many do I need?
ACH (Air Changes per Hour) is how many times the purifier filters the room's entire air volume per hour. 4-5 ACH is recommended for allergy relief. 2 ACH is the minimum for general air quality improvement.
How do I calculate my room's volume?
Room volume = length × width × ceiling height (in feet). Example: 15ft × 20ft room with 9ft ceiling = 2,700 cubic feet. Minimum CADR for 4 ACH = volume × ACH / 60 = 2,700 × 4 / 60 = 180.
Can one purifier cover my whole house?
Unless you have an HVAC-integrated whole-house system, no. Portable purifiers only clean the room they're in. One unit per bedroom + one for main living areas is the most effective setup.