Duct CFM Calculator
How to Use Duct CFM Calculator
Calculate the required cubic feet per minute (CFM) for your HVAC ductwork based on room size, type, and air velocity. Proper duct sizing ensures optimal airflow and system efficiency.
Understanding CFM
CFM (Cubic Feet per Minute) measures the volume of air flowing through your ductwork. The formula is: CFM = Duct Area (sq ft) x Air Velocity (FPM)
Air Changes Per Hour (ACH)
- Living Room: 6 ACH - Moderate ventilation
- Bedroom: 5 ACH - Comfortable sleeping environment
- Kitchen: 15 ACH - High ventilation for cooking
- Bathroom: 8 ACH - Moisture and odor control
- Office: 6 ACH - Good air quality for work
- Basement: 4 ACH - Basic ventilation
Recommended Air Velocities
- Supply Ducts: 700-900 FPM (feet per minute)
- Return Ducts: 500-700 FPM
- Main Trunk: 900-1200 FPM
- Branch Ducts: 600-800 FPM
Duct Sizing Guidelines
Properly sized ducts prevent system problems like poor airflow, excessive noise, and energy waste. Undersized ducts cause high velocity and noise, while oversized ducts reduce efficiency.
| Round Duct (inches) | CFM @ 800 FPM | Typical Use |
|---|---|---|
| 6" | 160 CFM | Small bedroom |
| 8" | 280 CFM | Medium bedroom |
| 10" | 440 CFM | Large room |
| 12" | 630 CFM | Main trunk |
Pro Tips
- Always verify calculations with local building codes
- Consider duct run length and number of bends
- Account for static pressure in your system
- Use smooth, rigid ducts when possible for better airflow
- Balance the entire system after installation
Cite this page as:
Daniel, P. Duct CFM Calculator. Available at: https://constructioncalculators.com/duct-cfm-calculator/. Accessed: October 25, 2026.