Duct Sheet Area Calculator
Estimate the four-face sheet-metal area of straight rectangular duct sections, then add a visible fabrication allowance for cuts, seams, hems and nesting losses.
Calculate duct sheet area
Sheet-metal area result
How the duct area calculation works
A rectangular straight duct with width W, height H and length L has four longitudinal faces. Their combined area is the duct perimeter multiplied by length.
Gross skin area = 2 × (W + H) × L × section count
Planning area = gross skin area × (1 + allowance ÷ 100)
Why area is different from stock-sheet count
Stock-sheet count depends on the sheet dimensions you buy and how panels can be nested. A nominal area result can therefore be lower than the actual quantity purchased when awkward cuts, seam development or flange details consume additional sheet.
What the allowance can cover
The user-entered allowance can represent cutting losses, seams, hems, fabrication additions and nesting inefficiency. Keep the value aligned with the actual shop process instead of treating the default as a universal rule.
Worked example
For a 600 × 400 mm duct section that is 3 m long:
One section = 2.0 × 3 = 6.0 m²
12 sections = 6.0 × 12 = 72.0 m²
With 8% allowance = 72 × 1.08 = 77.76 m²
Use the result with other takeoff steps
Pair the skin area with seam length, flange length, insulation area and fitting-specific surface estimates when building a broader ductwork material takeoff.
Frequently Asked Questions
Does this include duct ends?
No. The calculation covers the four longitudinal faces of straight rectangular duct sections.
Can I use inches or feet?
Yes. The selected dimensions are converted internally to metres.
Does this tell me exactly how many sheets to buy?
No. Exact sheet count requires stock-sheet dimensions and a cutting or nesting plan.
Does this calculate duct thickness?
No. Sheet thickness is a separate specification and should be determined from the applicable duct construction requirements.