Air Changes per Hour (ACH) Calculator

ACH expresses ventilation or circulation rate relative to space volume.

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Formula

ACH = CFM × 60 ÷ volume (ft³)

Example calculation

150 CFM in a 12 × 15 × 8 ft room (1,440 ft³) → 6.25 ACH.

Practical HVAC use

Ventilation and filtration checks.

Common mistakes

Using floor area instead of volume.

Related calculators

CFM from ACH

Pro

Calculate required ventilation airflow in CFM and L/s from a target ACH and room volume.

CFM ↔ L/s ↔ m³/h

Free

Convert CFM to litres per second and cubic metres per hour. Free airflow unit converter for HVAC ventilation and duct design.

Educational tool. Results are estimates from the stated formulas; always confirm with manufacturer data and the code adopted in your jurisdiction. All calculators