Duct thermal and materials
Use duct dimensions, lengths, and material properties to estimate sheet area and bare material weight.
Estimate straight round or rectangular duct sheet area, metal weight and material cost using actual thickness, density and your own allowance and price.
A straight duct material takeoff starts with the exterior wall perimeter extended over the run length. Round and rectangular shapes use different perimeter geometry, but both produce wall area without end caps. Multiplying the allowance-adjusted area by actual metal thickness and mass density gives a thin-sheet estimate of metal weight.
A gauge designation is not a physical thickness, and material density changes with the specified metal. The explicit allowance increases quantity once; it does not model a developed seam, reinforcement, or fitting. A price per pound converts this limited material estimate to a cost, rather than estimating a complete installed duct system.
Round area = πDL; rectangular area = 2(W + H)L; weight = area × (1 + allowance) × thickness × density
Bare area is the geometric starting quantity; allowance-adjusted area and weight are purchasing estimates under your fabrication assumptions. The cost reflects only Your material price.
Inputs: 12 in round duct, 10 ft long, 0.030 in thick, density 490 lb/ft³, zero allowance and a user-supplied price of $2/lb.
Calculation: Bare area is π × 1 ft × 10 ft = 31.416 ft². Sheet thickness is 0.030/12 = 0.0025 ft.
Result: About 38.485 lb and $76.969 of metal under these inputs. A 10% allowance raises weight to 42.333 lb.
Only lengths sharing the entered cross-section and material properties belong in one calculation. Separate differing sizes or thicknesses, then combine the resulting quantities outside this tool.
No. Straight wall metal is the modeled quantity. Flanges, reinforcement, supports, fittings, insulation, and other components need separate takeoffs; an allowance does not establish their actual weights.