1. Select the duct shape: rectangular or round.
2. Enter the width and height (for rectangular) or diameter (for round).
3. Enter the duct length.
4. Choose units for each input and desired output formats.
5. Click “Calculate Area” to see both cross-sectional and surface areas.

For rectangular ducts:

Cross-sectional Area = Width × Height
Surface Area = 2 × (Width + Height) × Length

For round ducts:

Cross-sectional Area = π × (Diameter / 2)²
Surface Area = π × Diameter × Length

• 1 inch = 2.54 cm
• 1 inch = 25.4 mm
• 1 foot = 12 inches
• 1 meter = 39.37 inches
• 1 ft² = 144 in²
• 1 m² = 1550.0031 in²

Reference: NIST Metric Conversion Card SP 365