6 Inch Duct Calculator
Calculate airflow capacity for 6 inch round ductwork. See CFM ratings at different velocities, recommended applications, and friction loss data for 6" HVAC ducts.
Airflow Capacity for 6" Round Duct
A 6 inch round duct has a cross sectional area of 28.3 square inches (0.196 sq ft). The table below shows the CFM airflow at different air velocities.
| Velocity (FPM) | Airflow (CFM) | Noise Level | Use Case |
|---|---|---|---|
| 600 FPM | 118 CFM | ✅ Quiet | Residential supply |
| 700 FPM | 137 CFM | ✅ Quiet | Residential supply |
| 800 FPM | 157 CFM | ⚠️ Moderate | Commercial supply |
| 900 FPM | 177 CFM | 🔊 May be noisy | Industrial |
Recommended Applications
Bathroom exhaust, small bedrooms, individual supply runs
At the standard residential friction rate of 0.08 in/wg per 100 feet, a 6 inch duct is ideal for delivering 137 CFM at a quiet 700 FPM velocity.
Quick Duct Sizing Formula
CFM for 6" Duct
CFM = (π/4) × (6/12)² × Velocity At 700 FPM: CFM = 0.1963 × 700 = 137 CFM