Calculate CFM (Cubic Feet per Minute), air changes per hour (ACH), and duct sizing for HVAC, ventilation, and air quality applications.
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CFM (Cubic Feet per Minute) is the standard unit for measuring airflow in HVAC and ventilation systems. Our calculator helps you determine proper ventilation requirements, air changes per hour, and duct sizing for any space.
CFM measures the volume of air flowing past a point in one minute. It's essential for sizing fans, air handlers, and ductwork in residential and commercial HVAC systems. Air Changes per Hour (ACH) indicates how many times the air in a room is completely replaced each hour. Ventilation targets follow ASHRAE standards (such as ASHRAE 62.1, which sets minimum outdoor-air rates and air changes for indoor air quality), so CFM and ACH size a system to code.
CFM & ACH Formulas
Size exhaust fans for moisture control (typically 8 ACH).
Calculate range hood CFM for effective cooking fume removal.
Ensure adequate airflow for IT equipment heat dissipation.
Size ventilation for dust and fume extraction.
Ensure adequate fresh air for healthy indoor environments.
Select properly sized fans and air handlers for your space.
Avoid over-ventilating which wastes energy and increases costs.
Meet ASHRAE 62.1/62.2 minimum ventilation rates and building-code exhaust requirements for permits and inspections.
ACH requirements vary by room type: bedrooms need 2-4 ACH, bathrooms 6-8 ACH, kitchens 7-8 ACH, and server rooms 10-20 ACH. Check ASHRAE guidelines for specific applications.
1 CFM = 0.472 liters per second (L/s) = 1.699 cubic meters per hour (m³/h). Our calculator automatically shows all conversions.
CFM = Velocity (ft/min) × Area (ft²). Higher velocities through smaller ducts or lower velocities through larger ducts can achieve the same CFM.
Use our duct size mode to calculate required cross-sectional area based on CFM and desired air velocity. Typical duct velocities range from 600-900 FPM for residential to 1000-1800 FPM for commercial.
No. This tool sizes airflow for HVAC and ventilation (room air changes and duct sizing). Engine/carburetor CFM is a separate calculation: CFM = CID × RPM × VE ÷ 3456, where CID is engine displacement in cubic inches and VE is volumetric efficiency.