Air Purifier Size Calculator: Find the Right CADR Rating
Use this calculator to find the correct air purifier size for your room. Calculate the required CADR (Clean Air Delivery Rate) based on your room’s dimensions and air quality needs.
List of the Top 10 Best Air Purifier:
Understanding Air Purifier Sizing: CADR and Room Coverage
Choosing the right size air purifier for your room is essential for improving indoor air quality, removing allergens, odors, smoke, and airborne particles efficiently. An underpowered air purifier will cycle air too slowly, while an oversized unit may cost more and be noisier than necessary.
What Is CADR?
CADR stands for Clean Air Delivery Rate. It's a standardized metric developed by the Association of Home Appliance Manufacturers (AHAM) that measures how quickly an air purifier can clean air. CADR is expressed in cubic feet per minute (CFM), and typically rated for:
- Smoke CADR – removes small particles like smoke and bacteria
- Dust CADR – removes fine particles like pollen or pet dander
- Pollen CADR – removes larger particles like plant pollen
Higher CADR means faster, more efficient air cleaning.
What Is ACH?
ACH stands for Air Changes per Hour. It refers to how many times the air in your room is fully filtered in one hour. For example, an ACH of 4 means your air is filtered once every 15 minutes. This is especially important for people with allergies, asthma, or during smoke events.
Recommended ACH by Usage
| Room Usage | Recommended ACH | Description |
|---|---|---|
| General Use | 4 ACH | Typical households with average air quality |
| Allergy Sufferers | 5–6 ACH | To reduce allergens effectively |
| Asthma / Smoke Exposure | 6–8 ACH | Helps reduce irritants and respiratory triggers |
| Medical / Clean Rooms | 10+ ACH | High-purity environments like clinics |
How to Calculate the Required CADR
The formula to calculate the required CADR for a room is:
CADR = (Room Volume × ACH) ÷ 60
Where:
- Room Volume = length × width × ceiling height (in feet)
- ACH = Air changes per hour, as desired
Room Size and CADR Examples
| Room Size | Room Volume (8 ft ceiling) | ACH | Required CADR |
|---|---|---|---|
| 10 x 10 ft | 800 cu ft | 4 | 53 CFM |
| 12 x 15 ft | 1,440 cu ft | 5 | 120 CFM |
| 20 x 20 ft | 3,200 cu ft | 6 | 320 CFM |
Types of Filters in Air Purifiers
The CADR alone doesn't determine air purifier performance. The filter type matters too:
- HEPA Filters: Remove 99.97% of airborne particles 0.3 microns in size
- Activated Carbon Filters: Trap gases, VOCs, smoke, and odors
- UV-C Light: Kills bacteria and viruses (effectiveness may vary)
- Ionizers: Emit ions that attract particles (may release ozone)
Noise and Placement
Larger CADR units may be louder at high speed. Choose a unit with multiple fan settings for flexibility. Place your air purifier in a central location, away from walls or furniture blocking airflow. Avoid corners, and keep doors/windows closed during operation.
Frequently Asked Questions
Can I use a purifier with lower CADR than recommended?
Yes, but air will clean slower. You'll get fewer air changes per hour and may not see much benefit during allergy or smoke events.
Is a higher CADR always better?
Not always. Higher CADR units clean faster but cost more, use more power, and are often noisier. Choose based on room size.
Can one air purifier clean multiple rooms?
Not effectively unless rooms are open to each other. Closed doors block airflow. Use one unit per enclosed room or get a whole-house system.
How often should I run my air purifier?
For best results, run it continuously on a low or medium setting. Many models have auto modes that adjust based on sensor readings.
How often should I change filters?
Most HEPA filters last 6–12 months. Carbon filters may need replacement every 3–6 months depending on usage and air quality.
Tips for Better Indoor Air Quality
- Keep windows closed during pollen season or wildfires
- Vacuum and dust regularly to reduce particle buildup
- Don’t smoke indoors
- Use exhaust fans in kitchens and bathrooms
- Replace HVAC filters on schedule
Conclusion
Using an air purifier that matches your room size and air quality needs can drastically improve your comfort, health, and sleep. This calculator gives you an accurate CADR target so you can choose the right purifier with confidence. For allergy sufferers, people with asthma, or those living in urban or smoky environments, it’s a smart and effective investment in your well-being.