Air changes per hour calculator
Required airflow from room volume and the air change rate.
Fill in the fields and the result will appear here automatically.
Converts a chosen air-change rate into volumetric airflow for a room with a known floor area and height. You supply the rate; the page does not prescribe a requirement for homes, kitchens or workplaces. An air change is an air volume equal to the room volume, rather than a guarantee that every part of the original air is completely replaced.
How it works
Formula and logic
V = A·h; Q = V·ACH. With area in m², height in m and ACH in 1/h, Q is in m³/h. Divide Q by 3.6 for L/s and by 60 for m³/min; the daily volume ratio is 24·ACH. All three inputs must be positive finite numbers.
Example
A 20 m² room with a 2.7 m ceiling at 3 air changes needs 162 m³/h.
Fields and units
- Room area — m²
- Ceiling height — m
- Air changes per hour — h⁻¹
How to use
- — Enter the area and height of the zone served by ventilation.
- — Use the required air-change rate from the applicable design or specification.
- — Compare the airflow with equipment performance at its operating resistance.
Method and limitations
- Calculation method
- Formula and logic
- Data or methodology source
- CDC/NIOSH: air-change rate, airflow and volume; not selection of a required rate
- Limitation
- You supply the rate; the page does not prescribe a requirement for homes, kitchens or workplaces. An air change is an air volume equal to the room volume, rather than a guarantee that every part of the original air is completely replaced.
FAQ
What does 3 air changes per hour mean?
In one hour the delivered or removed volume equals three room volumes. With mixing, this does not mean all original air disappears after twenty minutes.
Which rate should I choose?
It depends on use, pollutants, occupancy and applicable requirements. The default 3 is an example, not a universal standard.
Can this alone size a fan?
No. You also need airflow at system resistance, the supply/extract balance and room conditions. A nominal airflow rating alone does not establish these.
Does a suspended ceiling count?
Enter the volume actually served. Include the space above the ceiling separately if it participates in ventilation; this calculator does not determine that arrangement.