Square Footage to ACH Converter
What ACH rating do you actually get in your room? Calculate real-world air changes per hour based on your room size, purifier CADR, and real-world factors like air leakage and placement.
Real ACH Calculation
Account for air leakage, placement efficiency, and other real-world factors
Reality vs Claims
See the gap between manufacturer claims and actual performance
Use Case Guidelines
Understand what your ACH level is adequate for - health, allergies, odors
Room Dimensions & Purifier
Your Actual ACH Results
What This ACH Level Is Good For:
Reality vs Marketing Claims
Why There's a Gap
-51% performance reduction due to air leakage around filters (15%), suboptimal placement (15% efficiency loss), and real-world conditions that manufacturers don't account for in their room size claims.
Adjust for Real-World Factors
Recommendation
Outstanding air quality for the most sensitive individuals and extreme conditions.
ACH Guidelines by Use Case
- • Severe COPD/asthma
- • Immune compromised
- • Hospital rooms
- • Wildfire smoke
- • Moderate asthma
- • Heavy allergens
- • Smoking areas
- • Chemical sensitivity
- • General allergies
- • Pet owners
- • Urban air quality
- • Cooking odors
- • Dust control
- • Light odors
- • General freshness
- • Minimal allergens
Your current ACH: 8.5 - Excellent for medical conditions
Understanding Air Changes Per Hour (ACH)
What is ACH?
Air Changes per Hour (ACH) measures how many times the entire volume of air in a room is replaced with clean air every hour. It's calculated by dividing the clean air delivery rate by the room volume, then multiplying by 60.
Why ACH Matters More Than Room Size
Manufacturers often claim their purifiers can handle rooms of a certain size, but they rarely specify the ACH achieved. A 400 sq ft claim might deliver 2 ACH (minimal cleaning) or 6 ACH (excellent cleaning) depending on the purifier's power.
Real-World Performance Factors
Actual ACH is always lower than theoretical calculations due to air leakage around filters, suboptimal placement, room airflow patterns, and other factors that manufacturers don't account for in their claims.
Why Manufacturer Claims Fall Short
Perfect Lab Conditions
Room size claims assume perfect sealing, optimal placement, and no air leakage
Low ACH Standards
Many claims are based on just 2-3 ACH, which provides minimal air cleaning
No Health Context
Claims don't specify that health conditions require 4-8+ ACH for meaningful relief
Marketing Over Science
Bigger room size numbers sell better, regardless of actual air quality delivered
How to Use the ACH Calculator
Step-by-Step Instructions
Measure Your Room
Enter the length, width, and ceiling height of your room in feet.
Enter Purifier CADR
Input your air purifier's CADR rating (CFM) from the specifications.
Add Manufacturer Claim
Enter the room size the manufacturer claims this purifier can handle.
Adjust Real-World Factors
Set air leakage and placement efficiency based on your purifier quality and setup.
Interpret Results
Review your actual ACH and what it's adequate for.
Understanding Your Results
Actual ACH
Real air changes per hour accounting for air leakage and placement efficiency
Quality Level
Adequate/Inadequate For
Specific use cases your ACH level can and cannot handle effectively
Reality Gap
Percentage difference between manufacturer claims and your actual performance
Real-World Factors
Adjust air leakage (5-30%) and placement efficiency (60-95%) for your situation
5 Real-World ACH Reality Check Examples
Budget Purifier Reality
Setup:
- • Room: 16×12×8 ft (192 sq ft)
- • Purifier: 150 CFM CADR
- • Claim: "Covers 300 sq ft"
- • Budget unit: 25% air leakage
Reality Check:
- • Actual ACH: 1.8 (Poor)
- • Manufacturer implied: 3.1 ACH
- • Reality gap: 42%
- • 🚫 Barely provides any air cleaning
🎯 Better Choice:
Mid-Range Performance
Setup:
- • Room: 14×10×8 ft (140 sq ft)
- • Purifier: 246 CFM CADR
- • Claim: "Covers 400 sq ft"
- • Good sealing: 15% air leakage
Performance:
- • Actual ACH: 4.2 (Good)
- • Manufacturer implied: 4.6 ACH
- • Reality gap: 9%
- • ✅ Good for allergies, pets
🎯 This Model:
Large Room Challenge
Setup:
- • Room: 20×16×9 ft (320 sq ft)
- • Purifier: 300 CFM CADR
- • Claim: "Covers 500 sq ft"
- • Poor placement: 70% efficiency
Challenge:
- • Actual ACH: 2.1 (Fair)
- • Manufacturer implied: 3.2 ACH
- • Reality gap: 34%
- • ⚠️ Marginal for allergies
🎯 Size Up:
Premium Performance
Setup:
- • Room: 12×10×8 ft (120 sq ft)
- • Purifier: 350 CFM CADR
- • Claim: "Covers 540 sq ft"
- • Premium: 8% air leakage, center placed
Excellence:
- • Actual ACH: 8.2 (Excellent)
- • Manufacturer implied: 3.9 ACH
- • Reality gap: -110% (exceeds claims!)
- • ✅ Medical-grade air quality
🎯 Premium Choice:
Oversized Overkill
Setup:
- • Room: 10×8×8 ft (80 sq ft)
- • Purifier: 560 CFM CADR
- • Claim: "Covers 1000+ sq ft"
- • Medical unit: 5% air leakage
Overkill:
- • Actual ACH: 25.3 (Extreme)
- • Manufacturer implied: 3.4 ACH
- • Reality gap: -645% (massive overkill)
- • 🚀 Cleanroom-level air quality
🎯 When You Need This:
Key Takeaways from ACH Examples
Room Size Claims Mislead
Bigger room claims often mean lower ACH - prioritize CADR over room size
Smaller Rooms Get Higher ACH
Same purifier delivers much higher ACH in smaller spaces
Target 4+ ACH for Health
Anything below 4 ACH provides minimal health benefits
Air Purifiers by Target ACH Performance
Entry Level (2-4 ACH)
Basic air cleaning for small-medium rooms
Good Performance (4-6 ACH)
Effective for allergies, pets, general health
Excellent (6+ ACH)
Medical-grade performance for health conditions
🎯 How to Choose Your Target ACH
2-4 ACH is Adequate For:
• Light dust control and basic freshness
• Occasional cooking odors
• Very mild seasonal allergies
• General air improvement (no health issues)
6+ ACH is Essential For:
• Asthma, COPD, or respiratory conditions
• Severe allergies or immune issues
• Heavy pet dander or smoke exposure
• Wildfire season or pollution events
Important Reality Check
This calculator reveals the gap between marketing claims and real-world performance. Key factors that affect your actual ACH:
- • Air leakage around filters (5-30% depending on build quality)
- • Room placement and airflow patterns (60-95% efficiency)
- • Filter aging and loading over time
- • Room shape, furniture, and obstacles to airflow
Use this calculator to set realistic expectations and choose appropriately sized purifiers for your actual air quality goals, not marketing claims.