Air Changes Calculator

Calculate air changes per hour (ACH) from room dimensions and airflow rate.

Calculation Mode

Length (ft)

Width (ft)

Height (ft)

Airflow Rate (CFM)

Air Changes Per Hour

ACH

Room Volume

cubic feet

Volume (m3)

cubic meters

Airflow (L/s)

Airflow (m3/hr)

Bedroom: 2-4 ACH

Living Room: 3-6 ACH

Office: 4-10 ACH

Kitchen: 15-25 ACH

Bathroom: 6-10 ACH

Laboratory: 6-15 ACH

Hospital OR: 15-25 ACH

Clean Room: 20-600 ACH

Understanding Air Changes Per Hour

Air changes per hour (ACH) measures how many times the total volume of air in a space is replaced in one hour. The formula is:

ACH = (CFM x 60) / Room Volume (ft3)

CFM = (ACH x Room Volume) / 60

Higher ACH values indicate better ventilation. ASHRAE standards specify minimum ACH for different space types to ensure indoor air quality.

ASHRAE rates.

Duct size.

Cooling load.

Fan laws.

VAV sizing.

Dehumidification.