Air Changes Per Hour Calculator
Calculate air changes per hour from room volume and airflow rate for ventilation design with this free ACH calculator in your browser.
Enter Values
Minimum 0
Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.
How to use this calculator
- Enter the airflow (m³/h) and the room volume (m³).
- Read the air changes per hour.
How it works
ACH = airflow ÷ room volume — how many times the room's air is replaced each hour.
Worked example
300 m³/h in a 75 m³ room. = 4 ACH.
Common mistakes
- Mixing units — convert L/s to m³/h (× 3.6) first.
- Using the fan's free-air rating, not the installed airflow.
Frequently asked questions
What ACH should a room have?
It varies: living rooms ~0.5, bathrooms ~6–8, commercial kitchens 15+. Check the relevant standard.
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Cite this tool
Zerdly. (2026). Air Changes Per Hour Calculator. Retrieved from https://www.zerdly.com/tools/air-changes-per-hour-calculator/
Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.