How the calculation works
Simple volumetric air-change relationship.
Formula
Q = n × V; n = Q ÷ V
Worked example
Room5 m × 4 m × 3 m
Volume60 m³
Air changes6 h⁻¹
Expected airflow360 m³/h / 100 L/s
Free Mechanical / HVAC calculator
Air changes per hour and airflow calculator
Calculate required airflow from a chosen air-change rate or determine air changes from airflow and room volume.
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Calculation result
Formula
Assumptions and limitations
Assumptions
- The room volume is the effective air volume.
- The user selects the appropriate ACH target.
What this does not check
- Does not select ventilation criteria or assess occupancy and contaminants.
- Does not include ventilation effectiveness, pressure balance or duct losses.
Formula version: 1.0 · Last reviewed: 16 August 2026
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