CFM Calculator converts between airflow rate (L/s or m³/s) and CFM, and also calculates required airflow from ACH, floor area, and ceiling height. It helps HVAC designers size ventilation systems based on either known flow or desired air changes per hour.
About airflow. Airflow is the amount of air moved per unit time. In metric, it is expressed as liters per second (L/s) or cubic meters per second (m³/s). In imperial, it is measured in cubic feet per minute (CFM). Correct airflow ensures adequate ventilation, thermal comfort, and indoor air quality.
About ACH (air changes per hour). ACH represents how many times the entire volume of air in a space is replaced each hour. It depends on both the size of the space and the ventilation rate. Typical residential spaces use 0.5–2 ACH, while medical or laboratory spaces may require 6–12 ACH or more.
About room volume. To calculate airflow from ACH, the room’s volume must be known. Volume is area × height. Area is entered in m² or ft², and height in m or ft. The calculator converts all values to cubic meters (m³) internally to ensure consistency.
Conversion. The calculator has two modes: “From Flow” – converts between L/s (or m³/s) and CFM, and “From ACH” – calculates airflow from ACH × Volume / 3600.
Qm³/s = ACH × (Area × Height) / 3600
QCFM = Qm³/s ÷ 0.00047194745
QL/s = Qm³/s × 1000
- Example 1: 250 L/s → 0.25 m³/s → ≈ 530 CFM.
- Example 2: ACH = 6, Area = 50 m², Height = 2.7 m → Volume = 135 m³ → Q = 6 × 135 / 3600 = 0.225 m³/s → ≈ 478 CFM.
- Example 3: 1000 CFM → ≈ 0.472 m³/s → ≈ 472 L/s.
Corresponding tools. Use the HVAC Load Calculator to estimate heating and cooling loads, and the Duct Sizing Calculator to determine duct dimensions based on airflow. For quick unit conversions, try the Feet ⇄ Meters or CFM ⇄ L/s converters.
