HVAC Ductwork Takeoff Calculator
Estimate straight-duct LF, surface area, approximate metal weight, insulation, liner, fitting counts and hanger assemblies. Enter specified duct dimensions and gauge; this is a quantity tool, not duct sizing or design.
HVAC Ductwork Takeoff Calculator
Calculate straight duct LF, surface area, approximate sheet-metal weight, insulation, liner, fittings, hangers and fabricated sections.
Need a Complete HVAC Takeoff or Estimate?
Get drawing-based quantities for ductwork, fittings, insulation, equipment, diffusers and related mechanical scope.
HVAC Estimating ServicesHow to Use the Ductwork Calculator
- Add a duct run and choose Rectangular or Round.
- Enter the duct dimensions and straight length from the project documents.
- Enter the number of identical physical runs.
- Select the specified sheet-metal gauge and set the fabrication allowance.
- Enable external insulation or rectangular internal liner where applicable, then enter allowance and package coverage.
- Enter fitting types and counts per run.
- Set maximum hanger spacing where required.
- Optionally enter a fabricated straight-section length.
- Add other runs, calculate and review the detailed takeoff and gauge summary.
The calculator does not determine duct dimensions or required gauge. Its outputs are quantities for the geometry and estimating assumptions you enter.
Calculate Straight-Duct Surface Area
Rectangular duct
For width and height in inches: Perimeter (ft) = 2 × (Width + Height) ÷ 12. Multiply that perimeter by the straight length in feet to obtain duct surface SF.
A 24 × 12-in duct × 100 LF has a 6-ft perimeter and 600 SF of straight-duct surface. This rectangular duct calculator multiplies the quantity by the number of identical runs.
Round duct
Circumference (ft) = π × Diameter (in.) ÷ 12. Straight-duct surface SF equals circumference × length. An 18-in round duct × 100 LF has approximately 4.7124 ft of circumference and 471.24 SF of surface.
Fabrication Allowance and Approximate Duct Weight
Order/fabrication SF = net straight-duct SF × (1 + allowance% ÷ 100). The default 10% is editable; use the allowance appropriate to your estimating method. The 600-SF example becomes 660 SF at 10%.
User-selected gauge
Select gauge from the project requirements. This sheet metal duct calculator does not choose pressure class, required gauge or reinforcement. V1 uses the following approximate nominal galvanized-steel estimating weights, not certified manufacturer weights.
| Gauge | Nominal lb/SF |
|---|---|
| 30 | 0.641 |
| 28 | 0.764 |
| 26 | 0.886 |
| 24 | 1.127 |
| 22 | 1.372 |
| 20 | 1.617 |
| 18 | 2.107 |
Approximate weight = straight-duct SF × selected lb/SF. At 26 ga, 600 SF × 0.886 = 531.6 lb net. With 10% fabrication allowance, 660 SF × 0.886 = 584.76 lb. The interface displays these as approximately 532 lb net / 585 lb order.
Metal summary by gauge
Project results group fabrication/order SF and approximate weight by the selected gauge. This helps organize purchasing across multiple runs; it does not imply that gauges are interchangeable.
Duct Insulation and Internal Liner
External insulation
The duct insulation calculator uses straight-duct exterior surface area plus its own editable allowance. For 600 SF with 10% insulation allowance, the requirement is 660 SF. At a user-entered 100 SF/package, that rounds upward to 7 packages.
Package coverage is an estimating input. The tool does not determine required R-value or insulation thickness.
Rectangular internal liner
V1 offers a takeoff-level liner approximation for rectangular duct only: straight-duct surface area plus the entered liner allowance, rounded up to packages using your coverage. It is not an exact internal clear-dimension development. Round duct does not produce an internal-liner takeoff in V1.
Fittings, Hangers and Fabricated Sections
Fittings are counts only
Enter 90° elbows, 45° elbows, tees, wyes, reducers/transitions, offsets, end caps or Custom fittings. Counts multiply by the number of identical physical runs.
Fitting-development sheet-metal SF and weight are excluded from V1. Adding fittings increases fitting counts, not the straight-duct SF or weight quantities.
Hanger assemblies
V1 assumes hangers at both ends of each physical run, with intermediate spacing no greater than the entered maximum.
Hangers per run = ceil(run length ÷ maximum spacing) + 1. Here, ceil means round upward to the next whole number. A 100-LF run at 10-ft spacing has 11 hanger assemblies.
These are hanger locations/assemblies, not quantities of threaded rod, channel, anchors or strap.
Fabricated straight sections
Sections per run = ceil(run length ÷ entered fabricated section length). A 100-LF run using 5-ft sections gives 20 sections. Actual fabrication practices vary; the section length is an estimating assumption.
Multiple and Identical Physical Runs
An identical-run count represents separate physical runs. It multiplies straight LF, surface quantities and fitting counts while preserving hanger endpoints for each run. Three 100-LF runs are not treated as one continuous 300-LF duct for hanger purposes.
Three identical default runs produce 300 LF, 1,800 net SF, 1,980 order SF, 20 insulation packages, 33 hangers, 6 elbows and 3 reducers. Add separate run entries when dimensions, gauge or estimating assumptions differ.
Worked Example: SA-1 Supply Duct
Use one rectangular 24 × 12-in run, 100 LF long, at 26 ga. Set metal allowance to 10%, enable external insulation with 10% allowance and 100 SF/package, and use 10-ft maximum hanger spacing. Enter two 90° elbows and one reducer.
| Takeoff item | Default result |
|---|---|
| Net straight-duct area | 600 SF |
| Order/fabrication area | 660 SF |
| Approximate net weight | 532 lb displayed (531.6 lb calculated) |
| Approximate order weight | 585 lb displayed (584.76 lb calculated) |
| External insulation | 660 SF / 7 packages |
| Hanger assemblies | 11 |
| Fittings | 2 elbows + 1 reducer |
What V1 Does Not Calculate
This ductwork takeoff calculator does not calculate CFM/airflow sizing, friction loss, static pressure, velocity, equivalent diameter, ductulator sizing, required gauge, pressure class or SMACNA reinforcement.
Fitting-development SF, elbow radius geometry, transition development, flex duct and spiral fitting takeoff are excluded. It does not take off dampers, diffusers/grilles, VAV boxes or HVAC equipment, nor threaded rod LF or trapeze/channel material. Labor, productivity and pricing are also outside V1.
Frequently Asked Questions
How do I calculate ductwork square footage?
Multiply straight-duct perimeter or circumference in feet by its straight length, then multiply by the number of identical runs. Keep fitting-development material separate.
How do I calculate rectangular duct surface area?
Add width and height in inches, multiply by two and divide by 12 for perimeter in feet. Multiply by length in feet. A 24 × 12-in, 100-LF run has 600 SF of surface.
How do I calculate round duct surface area?
Multiply π by diameter in inches, divide by 12, then multiply by straight length in feet. An 18-in diameter, 100-LF run has approximately 471.24 SF.
Does this calculator size HVAC ducts from CFM?
No. Enter duct dimensions already established for the project. It is a takeoff tool, not an airflow or duct-design calculator.
Does it determine the required sheet-metal gauge?
No. You select gauge according to project requirements. The selected gauge supplies an approximate nominal weight coefficient only.
How is ductwork weight calculated?
The duct weight calculator multiplies straight-duct SF by the selected nominal lb/SF. Order weight uses the area with fabrication allowance; fitting-development weight is excluded.
Can it calculate duct insulation?
Yes. External insulation uses straight-duct surface area plus an editable allowance and rounds up to your package coverage. Rectangular internal liner is available as a separate takeoff approximation.
How are duct hangers calculated?
Each physical run receives hangers at both ends, with intermediate spacing no greater than your maximum. A 100-LF run at 10-ft spacing gives 11 assemblies.
Are fittings included in sheet-metal square footage?
No. V1 reports entered fitting counts separately. Fitting-development surface area and weight are not added to straight-duct quantities.
Can I calculate multiple duct runs?
Yes. Add separate entries for different runs or use the identical-run count for repeats. Fittings and hanger endpoints are counted for each physical run.