Air Duct Velocity Calculator

The Formula

The formula for calculating air velocity in a duct is:

\[Velocity (fpm) = \frac{Flow Rate (CFM)}{Duct Area (sq ft)}\]

Where:

• Velocity: The speed of air in the duct (in feet per minute, fpm)
• Flow Rate: The volumetric flow rate of air (in cubic feet per minute, CFM)
• Duct Area: The cross-sectional area of the duct (in square feet)

Calculation Steps

1. Calculate the duct area in square feet: Area = (Width × Height) ÷ 144
2. Divide the flow rate by the duct area: Velocity = Flow Rate ÷ Area

Example Calculation

Let's calculate the air velocity for a duct with dimensions 12" × 8" and a flow rate of 1000 CFM:

1. Duct Area = (12 × 8) ÷ 144 = 0.6667 sq ft
2. Velocity = 1000 ÷ 0.6667 = 1500 fpm

Visual Representation

This visual shows the air velocity in a duct based on our example calculation.