Calculate the exact CADR (Clean Air Delivery Rate) you need based on your room dimensions and desired air changes per hour. Get instant recommendations for the best air purifiers that match your requirements.
Measure the longest wall of your room
Measure the perpendicular wall
Standard ceiling height is 8 feet
Air changes per hour - higher is better for allergies
Try adjusting your room size or ACH requirements to see recommendations.
Our ACH (Air Changes per Hour) calculator helps you determine the exact CADR rating you need for optimal air purification in your space. Follow these simple steps to get accurate, personalized recommendations for your room.
Use a measuring tape to get precise dimensions. Measure the length (longest wall),width (perpendicular wall), and ceiling height. Round to the nearest half-foot for best results.
Select your desired air changes per hour based on your needs:
The calculator instantly shows your required CADR rating, room volume, and air turnover time. Use these numbers when shopping for air purifiers.
Browse our curated selection of air purifiers that match your calculated requirements. Each recommendation includes detailed specs and real user reviews.
The calculator provides several key metrics to help you choose the right air purifier. Here's what each number means and how to use this information when shopping for your ideal air cleaning solution.
This is the most important number - it tells you the minimum Clean Air Delivery Rate (in CFM) your air purifier needs to achieve your desired ACH.Always choose a purifier with a CADR rating equal to or higher than this number.
Example: If the calculator shows 240 CFM CADR, look for air purifiers rated at 240+ CFM. A 300 CFM unit would work excellently and give you extra cleaning power.
This shows the total cubic feet of air in your room (length × width × height). Larger rooms need more powerful air purifiers. This helps you understand why bigger spaces require higher CADR ratings.
Rule of thumb: Divide room volume by 7.5 for a quick CADR estimate for standard 4 ACH cleaning.
This tells you how long it takes for your air purifier to filter all the air in your room once. Lower times mean faster air cleaning:
Air Changes per Hour (ACH) is a crucial measurement that determines how many times the air in your room gets completely filtered and replaced each hour. Understanding ACH helps you choose the right level of air purification for your specific health needs and environmental conditions.
ACH measures the volume of air filtered divided by room volume. If your room has 1,000 cubic feet of air and your purifier processes 4,000 cubic feet per hour, you're getting 4 ACH.
Higher ACH rates mean pollutants, allergens, and particles are removed faster and more thoroughly. This is especially important for people with allergies, asthma, or respiratory sensitivities.
Medical facilities often use 6-12 ACH, while residential spaces typically need 4-6 ACH. The EPA recommends at least 5 ACH for homes with allergy sufferers.
| ACH Level | Best For | Turnover Time | Use Cases |
|---|---|---|---|
| 2-3 ACH | Basic air cleaning | 20-30 minutes | Minimal allergies, general air freshening |
| 4-5 ACH | Most residential spaces | 12-15 minutes | Standard homes, light allergies, general health |
| 5-6 ACH | Allergy sufferers, pet owners | 10-12 minutes | Pets, moderate allergies, smoke exposure |
| 6+ ACH | Severe allergies, asthma | Under 10 minutes | Severe asthma, immunocompromised, wildfire smoke |
While higher ACH is generally better for air quality, consider these practical factors:
See how the ACH calculator works with these detailed examples from different room types and scenarios. Each example shows the complete calculation process and explains why specific ACH levels were chosen.
10 × 10 ft bedroom with 8 ft ceiling
15 × 12 ft bedroom for allergy sufferer
20 × 18 ft living room with high ceiling
14 × 12 ft room with pets (dander control)
12 × 11 ft nursery for baby with allergies
See how our calculator helps different users determine their ideal CADR and ACH levels
Needs 80 CFM CADR minimum. Air completely filtered every 12 minutes. Reduces allergen exposure by 95% within first hour.
Needs 270 CFM CADR minimum. Complete air turnover every 10 minutes. Effectively controls pet dander and odors.
Needs 179 CFM CADR minimum. Air filtered every 7.5 minutes. Medical-grade clean air for breathing comfort.
Needs 333 CFM CADR minimum. Consider 2 units (170 CFM each) for better coverage and circulation.
Needs 113 CFM CADR minimum. Clean air every 8.5 minutes. Choose whisper-quiet models for undisturbed sleep.
Every room is unique. Get precise CADR requirements based on your exact dimensions and air quality needs.
Expand your air purifier knowledge with these helpful tools and educational resources. Get a complete understanding of air purification to make the best choice for your home.