Air Changes per Hour (ACH) Calculator

ASHRAE Air Changes Per Hour (ACH)

Air Changes per Hour (ACH) is a ventilation metric defined by ASHRAE as the number of times the entire volume of air within a space is replaced in one hour.

ACH Formula

ACH = (CFM × 60) / Room Volume (in cubic feet)

• CFM = Cubic Feet per Minute (airflow rate)
• Room Volume = Length × Width × Height

ACH Calculator

Select Space Type: Office Conference Room Restaurant Class Room Laboratory Hospital Room Patient Room Operating Room Intense Care Unit Warehouse Welding Shop Auditorium Theater Living Room Kitchen Bathroom Custom Select Units: Metric (meters, CMH) Imperial (feet, CFM) Room Length: Room Width: Room Height: Air Flow Rate:

* According to ASHRAE Standard 62.1, ACH recommendations vary by occupancy type.
Ensure the calculated ACH aligns with the minimum ventilation requirements for your application.

ASHRAE Guidelines for ACH

Space Type	Recommended ACH (Typical)	Standard
Office (General)	2 – 4 ACH	ASHRAE 62.1
Classrooms (K-12)	3 – 6 ACH	ASHRAE 62.1
Conference Rooms	4 – 10 ACH	ASHRAE 62.1
Patient Rooms (Hospitals)	6 ACH (min)	ASHRAE 170
Operating Rooms (Hospitals)	15 – 20 ACH	ASHRAE 170
Bathrooms	6 – 10 ACH	ASHRAE 62.1
Laboratories (General)	6 – 12 ACH	ASHRAE 62.1
Isolation Rooms (Hospitals)	12 ACH (min)	ASHRAE 170

References:

• ASHRAE Standard 62.1 – Ventilation for Acceptable Indoor Air Quality
• ASHRAE Standard 170 – Ventilation of Health Care Facilities
• ASHRAE Handbook – Fundamentals