Air Changes Per Hour Calculator

This tool calculates how many times the air in a room is replaced each hour based on the room's size, ceiling height, and airflow rate.

ACH Calculator

Enter the floor area of the room.
Set the height of the room’s ceiling in feet (ft).
Input the airflow rate of the air purifier.

Air changes per hour (ACH): 0 ACH

Air Changes Per Hour (ACH) is a measurement used in indoor air quality management to indicate how many times the air within a defined space is changed/moved through the filter media (usually an air purifier's filter).

Formula: ACH = (Airflow in CFM x 60) / (Room Area x Ceiling Height)

Condition Required minimum Air Changes per Hour (ACH)
Normal conditions 2
AHAM standard (recommended for many conditions) 4.8
Smoke or VOCs 8