Duct Area Calculator

Calculate round or rectangular duct area in square feet using diameter, or width and height in inches.

Calculator

Duct Shape

Width (inches)

Height (inches)

Duct Area

0.00 sq ft

Enter values above and click calculate.

How It Works

This calculator finds the cross-sectional area of a duct in square feet. Duct area is a key input for air velocity calculations and duct sizing — knowing the area lets you determine how fast air is moving through a system or whether a duct is properly sized for the required airflow.

Rectangular: Area (sq ft) = (Width × Height) ÷ 144

Round: Area (sq ft) = π × (Diameter ÷ 2)² ÷ 144

Where:
Width = duct width in inches
Height = duct height in inches
Diameter = duct diameter in inches
144 = converts square inches to square feet (12 × 12)
π = 3.14159 — used to calculate the area of a circle

Common examples:
A 24 × 12 rectangular duct = 2.00 sq ft
A 12" round duct = 0.79 sq ft
A 16" round duct = 1.40 sq ft

Tip: Use this result directly in the Air Velocity calculator to check if air is moving within the recommended range for your duct type.