Occupational Safety, Health, and Environmental (OSHE) BlogOccupational Safety, Health, and Environmental (OSHE) BlogAir Change per Hour (ACH) Calculator
ACH Ventilation Tool
Calculate air change rates for proper ventilation assessment and indoor air quality management.What is Air Change per Hour (ACH)?
Air Change per Hour (ACH) is a measure of how many times the air in a room is completely replaced with fresh air in one hour. It's a crucial metric for assessing ventilation effectiveness and indoor air quality in buildings and facilities.
ACH is calculated by dividing the total air flow rate by the room volume, providing insight into how well a space is ventilated and whether it meets health and safety standards for indoor air quality.
ACH Formula
Imperial Units
ACH = (CFM × 60) ÷ Room Volume (ft³)
Metric Units
ACH = Airflow Rate (m³/h) ÷ Room Volume (m³)
Where:
CFM = Cubic Feet per Minute
m³/h = Cubic Meters per Hour
m³/h = Cubic Meters per Hour
Ventilation Standards
Recommended ACH by Room Type
Offices:6-8 ACH
Classrooms:8-12 ACH
Hospitals:12-15 ACH
Laboratories:15-20 ACH
Cleanrooms:20-60 ACH
Activity Level Factors
Low Activity:4-6 ACH
Moderate Activity:6-10 ACH
High Activity:10-15 ACH
Very High Activity:15+ ACH
Ventilation Level Classification
Poor Ventilation< 2 ACH
Low Ventilation2 - 6 ACH
Adequate Ventilation6 - 12 ACH
Good Ventilation12 - 20 ACH
High Ventilation> 20 ACH
ACH Calculator
Total room volume
Total air supply/exhaust rate