You can easily calculate the Air Changes Per Hour (**ACH** or **ACPH**) using:

- Airflow rate of your Air Purifier / HVAC
*(CFM or m³/h)*, - Room area
*(square footage or L x W)*, and - Ceiling height.

Calculate the Air Changes Per Hour (**ACH** or **ACPH**) from the calculator below:

Formula:

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

Calculate the required CADR for your room: CADR Calculator

Benoit says

If you have two air purifiers what’s the effect on the air changes per hour and time to clean the room.

Thanks

Reviewsofairpurifiers says

For more than one air purifier, use the cumulative airflow rate (CADR) to calculate the air changes per hour. If you have two air purifiers, the number of Air Changes per Hour (ACH) will be doubled, which means it will take half the time to clean the room.