ACH Calculator (Air Changes per Hour)

What is ACH?

ACH (Air Changes per Hour) tells you how many times the entire air volume of a room is replaced in one hour. It is a critical metric for indoor air quality in homes, offices, hospitals, and cleanrooms.

ACH Formula

Formula: ACH = (CFM × 60) ÷ (Length × Width × Height)

Where:
CFM = Airflow in cubic feet per minute
Room Volume = Length × Width × Height (cubic feet)

Example Calculation

Suppose a room is 20 ft × 15 ft × 10 ft with 200 CFM airflow:
Volume = 20 × 15 × 10 = 3,000 cu ft
ACH = (200 × 60) ÷ 3000 = 4 ACH
✅ This means the room air is replaced 4 times per hour.

Recommended ACH Values

Space Type	Recommended ACH
Bedroom	5 – 6 ACH
Office	6 – 8 ACH
Classroom	6 – 12 ACH
Kitchen	8 – 12 ACH
Hospital Room	12 – 20 ACH

Frequently Asked Questions

Why is ACH important?

It ensures proper ventilation, removes contaminants, and maintains healthy indoor air quality.

How can I increase ACH?

You can increase ACH by improving fan capacity, adding more air diffusers, or reducing room volume (partitioning large spaces).

What happens if ACH is too low?

Low ACH means poor air quality, risk of odor build-up, and higher chances of airborne infections.