Air Changes Per Hour Calculator
Ventilation rate for a room.
Enter your values
ⓘ Live results
Results
- Air changes per hour
- 5.56
- Room volume
- 2,700 ft³
- CFM for target ACH
- 270
- Status
- Below target
Quick answer
Air changes per hour measures how many times a room's air volume is replaced each hour.
ACH = CFM × 60 ÷ room volume
How to use the Air Changes Per Hour Calculator
- 1Enter the room dimensions.
- 2Enter the measured or designed airflow.
- 3Set the ACH target for the room type.
Worked example
Using the values the calculator loads with:
Inputs
- Room length20 ft
- Room width15 ft
- Ceiling height9 ft
- Airflow250 CFM
- Target ACH6
Results
- Air changes per hour5.56
- Room volume2,700 ft³
- CFM for target ACH270
- StatusBelow target
Frequently asked questions
What ACH does a kitchen need?
Typically 7–8; bathrooms 6–8 and offices 4–6.
Does higher ACH cost more?
Yes — in fan energy and conditioned air lost.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.