Ductwork Takeoff: Fittings, Gauge and Sheet Metal Weight
A ductwork takeoff measures every duct run and counts every fitting and air device on an HVAC (heating, ventilation and air conditioning) drawing, then turns the duct into pounds of sheet metal by its gauge.
Used on commercial, industrial and data center mechanical bids, wherever the sheet metal scope is priced by weight.
How a Ductwork Takeoff Is Done
Every duct size is taken off separately, because each one uses a different amount of sheet metal and often a different gauge. The takeoff runs in three steps.
Measure the Straight Duct
The estimator traces each duct run on the plan and records its length for every size, such as 24 x 12 inch rectangular or 10 inch round, keeping rectangular, round, spiral and oval duct apart.
Count Fittings and Air Devices
Every elbow, transition, offset, tee and branch takeoff is counted by size, along with dampers, diffusers, grilles and registers from the air device schedule. Fittings take more labor than straight duct, so each one is listed on its own.
Turn Duct Into Pounds
The estimator works out the surface area of each run, multiplies it by the weight per square foot of its gauge and adds an allowance for seams and waste. That weight drives the material price and much of the labor.
Duct Gauge and Sheet Metal Weight
A lower gauge number means thicker metal. Larger ducts and higher pressure classes need thicker sheet, so the gauge steps up as the duct gets bigger. The project specification sets the gauge, usually following SMACNA (Sheet Metal and Air Conditioning Contractors' National Association) standards.
- Weight per square foot rises with every step down in gauge number.
- Rectangular duct weight comes from its perimeter times its length.
- 100 feet of 24 x 12 inch duct at 24 gauge weighs about 694 pounds before seams and waste.
| Gauge | Thickness (in) | Weight (lb per sq ft) |
|---|---|---|
| 26 | 0.0217 | 0.906 |
| 24 | 0.0276 | 1.156 |
| 22 | 0.0336 | 1.406 |
| 20 | 0.0396 | 1.656 |
| 18 | 0.0516 | 2.156 |
| 16 | 0.0635 | 2.656 |
Fittings Are Where Duct Bids Go Wrong
Straight duct is easy to measure, but a mechanical package can carry thousands of fittings, air devices and hangers, each priced on its own. A full ductwork takeoff lists straight duct by size and gauge, every fitting and air device, the gaskets, bolts and welds on flanged or welded duct, plus insulation, liner and supports.
| 24 x 12 duct, 24 ga | 100 ft |
| Elbows | 4 |
| Transitions | 2 |
| Branch takeoffs | 3 |
| Diffusers | 6 |
| Straight duct weight | 694 lb |
The Takeoff AI reads the HVAC drawings, measures duct length and counts every fitting, gasket, bolt and weld. It returns the material takeoff (MTO) and labor takeoff (LTO) with a priced bill of materials, and highlights each item on the drawing with an accept or reject option.
- Duct length measured by size, with every fitting counted
- MTO, LTO and a priced bill of materials, traced to the sheet
More Mechanical Bids, Fewer Estimators to Count Them
Mechanical scopes on data center and industrial projects carry large duct packages, and each one has to be counted fitting by fitting. With fewer estimators carrying more bids each year, the hours spent tracing duct runs are hours taken from pricing, risk and the next bid. A takeoff that measures and counts the duct for you gives that time back.
“A missed fitting costs more than a missed foot of straight duct.”
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Ductwork Takeoff: Fittings, Gauge and Sheet Metal Weight
What is a duct takeoff?
A duct takeoff is the measurement of every duct run and the count of every fitting and air device on an HVAC drawing. It gives the sheet metal weight and quantities used to price the duct scope.
How do you calculate ductwork weight?
Work out the surface area from the duct's perimeter and length, multiply it by the weight per square foot for its gauge, then add an allowance for seams and waste.
How is duct gauge chosen?
Gauge depends on the duct size and its pressure class. The project specification sets it, usually following SMACNA standards, and larger or higher pressure duct needs thicker sheet.
Are fittings priced the same as straight duct?
No. Fittings take more labor per pound than straight duct, so estimators count them separately by size and price them per piece or with labor units.
Can software do a ductwork takeoff?
Yes. The Takeoff AI measures duct length, counts fittings, gaskets, bolts and welds, and returns the MTO, LTO and a priced bill of materials, with every number traced to the drawing.