Sheet metal is priced by weight, but labor is driven by fittings. A run full of elbows and transitions takes far longer to fabricate and hang than a straight trunk of the same weight. A good duct takeoff captures both.
How this guide was prepared: written and reviewed by the Design Estimation estimating team, led by founder Austin Smith (7+ years in construction estimating) and backed by ASPE Certified Professional Estimators. Quantities are measured from real drawings and checked by a person; software is used for speed, not judgment.
What a Duct Takeoff Includes
| Item | How it is measured |
|---|---|
| Rectangular duct | Linear feet by size, converted to pounds by gauge |
| Round and spiral duct | Linear feet by diameter |
| Fittings | Elbows, tees, offsets, transitions and takeoffs, each |
| Dampers | Volume, fire, smoke and combination dampers by size |
| Access doors | Each |
| Flex duct and connectors | Linear feet and each |
| Air devices | Diffusers, registers and grilles (sometimes in a separate scope) |
| Insulation and liner | Square feet by thickness |
| Hangers and supports | Each or per length of duct |
| Sealing and testing | By pressure class and specification |
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How Duct Weight Is Calculated
- Measure each run’s length by size.
- Find the duct perimeter from its dimensions.
- Multiply perimeter by length to get surface area.
- Apply the gauge from the specification or SMACNA tables for the duct size and pressure class.
- Convert area to pounds using the weight per square foot for that gauge, and add seams and reinforcement.
Formula for rectangular duct: weight (lb) = 2 × (width + height, in ft) × length (ft) × weight per sq ft for the gauge. For round duct, use π × diameter (ft) × length. Most estimators then add an allowance for seams, joints and reinforcement.
Galvanized Sheet Weight by Gauge
| Gauge | Weight (lb per sq ft) | Typical use (always follow the specification) |
|---|---|---|
| 26 | 0.906 | Small residential branch ducts |
| 24 | 1.156 | Residential trunks and small commercial ducts |
| 22 | 1.406 | Medium commercial ducts |
| 20 | 1.656 | Larger ducts and higher pressure classes |
| 18 | 2.156 | Large ducts and industrial exhaust |
| 16 | 2.656 | Very large or high-pressure ducts |
The required gauge depends on the longest side of the duct, the pressure class and the reinforcement spacing, so take it from the project specification and the SMACNA HVAC Duct Construction Standards rather than from a rule of thumb.
Worked Example: One Duct Run
| Step | Calculation | Result |
|---|---|---|
| Duct size and length | 24″ × 12″ rectangular, 100 ft | – |
| Perimeter | 2 × (2 ft + 1 ft) | 6 ft |
| Surface area | 6 ft × 100 ft | 600 sq ft |
| Weight | 600 sq ft × 1.156 lb (24 gauge) | 693.6 lb |
| Allowance | +15% for seams, joints and reinforcement (example) | About 798 lb |
Fittings on the same run are counted separately. Two elbows and a transition add little weight but can take more shop and field hours than the 100 ft of straight duct, which is why a good takeoff reports both pounds and fitting counts.
Turning Pounds into a Price
Sheet metal contractors usually price ductwork as total pounds × fabricated cost per pound, plus fitting and accessory counts × labor units, plus insulation, hangers and sealing. Cost per pound varies widely with shop rates, union labor, duct size and region, so use your own shop and field rates rather than a national average. If you would rather not measure it yourself, our duct takeoff services deliver pounds by gauge and fitting counts in 24–48 hours.
What Drives Sheet Metal Labor
- Number and type of fittings.
- Duct size (large ducts need lifts and more crew).
- Installation height and access.
- Pressure class and sealing requirements.
- Coordination with other trades in tight ceilings.
Regional Considerations
In humid climates, insulation, vapor barriers and condensate control matter more. In seismic regions, duct supports may need bracing. Local labor rates and union requirements also change pricing.
What You Receive
- Duct quantities by size, gauge and system, with total pounds.
- Fitting, damper and accessory counts.
- Insulation quantities and labor hours.
- Marked-up mechanical drawings.
For the full HVAC scope, see our HVAC estimating guide and mechanical and HVAC estimating services. For fabrication layouts, see our HVAC shop drawings guide. Send your plans for a duct takeoff.
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Standards referenced: SMACNA HVAC Duct Construction Standards (gauge and reinforcement tables). Always check the edition adopted for your project.
Frequently Asked Questions
Quick answers to the questions contractors ask us most.
What is a duct takeoff?
A duct takeoff measures all ductwork, fittings and accessories on the mechanical drawings and converts sheet metal to weight for pricing.
How is ductwork priced?
Material is usually priced by the pound, while labor depends heavily on fittings, size and installation conditions.
Do you count fittings separately?
Yes. Elbows, tees, transitions and takeoffs are counted separately because they drive fabrication and installation time.
Do you include duct insulation?
Yes. Duct wrap and liner are measured by area and thickness when they are in scope.
How long does a duct takeoff take?
Most duct takeoffs are delivered in 24 to 48 hours, depending on building size.
Are duct takeoffs prepared by AI or human estimators?
Our duct takeoffs are prepared and reviewed by experienced human estimators, with software used to speed up measuring.
How do you calculate duct weight?
Multiply the duct perimeter by its length to get surface area, then multiply by the weight per square foot for the gauge. A 24 by 12 inch duct, 100 ft long, in 24 gauge weighs about 694 lb before an allowance for seams and reinforcement.
What gauge is HVAC ductwork?
Most galvanized HVAC ductwork is 26 to 18 gauge. The exact gauge depends on duct size, pressure class and reinforcement, and is set by the specification and SMACNA standards.
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