8 Inch Duct Calculator
Calculate airflow capacity for 8 inch round ductwork. See CFM ratings at different velocities, recommended applications, and friction loss data for 8" HVAC ducts.
Airflow Capacity for 8" Round Duct
A 8 inch round duct has a cross sectional area of 50.3 square inches (0.349 sq ft). The table below shows the CFM airflow at different air velocities.
| Velocity (FPM) | Airflow (CFM) | Noise Level | Use Case |
|---|---|---|---|
| 600 FPM | 209 CFM | ✅ Quiet | Residential supply |
| 700 FPM | 244 CFM | ✅ Quiet | Residential supply |
| 800 FPM | 279 CFM | ⚠️ Moderate | Commercial supply |
| 900 FPM | 314 CFM | 🔊 May be noisy | Industrial |
Recommended Applications
Bedrooms, offices, standard residential supply branches
At the standard residential friction rate of 0.08 in/wg per 100 feet, a 8 inch duct is ideal for delivering 244 CFM at a quiet 700 FPM velocity.
Quick Duct Sizing Formula
CFM for 8" Duct
CFM = (π/4) × (8/12)² × Velocity At 700 FPM: CFM = 0.3491 × 700 = 244 CFM