Building & DIY

Air Changes Per Hour Calculator (ACH from CFM)

Compute air changes per hour for a room from its volume and the airflow through it. Enter dimensions and CFM or m³/h, and compare the result to ASHRAE targets.

How to use
  1. Enter the room dimensions or its volume.
  2. Enter the airflow in CFM or m³/h.
Estimates only, allow for waste and confirm against local building codes and supplier specs.
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Reference ranges

Room typeTypical target ACH
Office4 – 8
Kitchen7 – 15
Gym6 – 10
Hospital room6 – 12

Common questions

How do I calculate air changes per hour?

Multiply CFM by 60 and divide by the room volume in cubic feet. A 200 CFM fan in a 1,200 cubic-foot room gives 10 ACH.

What is a good ACH for a bedroom?

Around 4 to 6 air changes per hour is comfortable for a living space. Kitchens and bathrooms need more.

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