Air Changes per Hour (ACH) Calculator
Calculate ACH from room size and airflow rate
Calculator
Select whether you want to calculate ACH using room dimensions or known volume.
About the ACH Calculator
The Air Changes per Hour (ACH) Calculator helps you determine how many times the air inside a room is replaced every hour based on room volume and airflow rate. This tool is essential for HVAC engineers, indoor air quality specialists, facility managers, and anyone evaluating ventilation performance in residential, commercial, or industrial spaces.
What You Can Calculate
- Room Volume: Automatically computed from room dimensions or entered directly if already known, in ft³ or m³.
- Airflow Rate: Convert and calculate airflow in CFM (ft³/min) or m³/h.
- Air Changes per Hour (ACH): The number of complete air replacements occurring in a room each hour.
Formulas Used in the Calculator
This calculator uses standard HVAC ventilation formulas to determine ACH:
- Room Volume (from dimensions): Volume = Length × Width × Height
- Air Changes per Hour: ACH = (Airflow × 60) ÷ Room Volume
- Unit Conversions:
1 m = 3.28084 ft
1 m³ = 35.3147 ft³
1 m³/h = 1.699 CFM
How to Use the Calculator
- Choose whether you want to enter room dimensions or a known room volume.
- Enter the airflow rate in either CFM or m³/h.
- The calculator will instantly compute the room volume (if needed), convert units, and display the ACH value.
Applications of ACH
ACH is a critical metric for evaluating the effectiveness of ventilation systems. Higher ACH values generally indicate better airflow, improved contaminant removal, and healthier indoor environments. It is widely used in HVAC design, ASHRAE compliance, cleanrooms, hospitals, laboratories, schools, and industrial ventilation.