Sheet metal duct calculator: weight and price per foot.
Enter duct runs by size, length and gauge. The calculator converts girth to square feet of sheet, applies the galvanized weight per square foot, adds seams and reinforcement, and turns your $/lb into a price per foot.
Send one plan set. See what the AI extracts and what it flags for review. No obligation.
- Rectangular and round
- 26 to 16 gauge
- Price per foot or per meter
1 · Duct runs W × H or diameter, in inches
2 · Allowance & prices
Live formula
Save your results
Copy these results, then add your approved sample files in the trial brief.
Estimates only. Check every default against your spec, supplier data and crew records before you bid.
Standard formulas, shown on the page.
Nothing hidden. These are the same steps an estimator runs on a takeoff sheet.
1. Girth to sheet area
A rectangular duct uses its full perimeter of sheet: 2 × (width + height). Round duct uses π × diameter. Convert inches to feet and multiply by length.
2. Gauge weight
Multiply square feet of sheet by the weight per square foot for the galvanized gauge the spec assigns to that duct size and pressure class.
3. Seams and reinforcement
Lock seams, transverse joints, reinforcement and hangers add weight beyond the flat girth. Many shops carry a percentage.
4. Price per foot
Price the pounds at your material and shop rates, then divide by the linear footage for a price per foot.
Every default is cited or editable.
Replace any of these with your spec, supplier data sheet or job-cost history. The calculator recalculates instantly.
| Input | Default | Source |
|---|---|---|
| 26 / 24 / 22 / 20 / 18 / 16 ga | 0.906 / 1.156 / 1.406 / 1.656 / 2.156 / 2.656 lb/sq ft | Galvanized steel gauge and weight chart (Continental Steel) |
| Seam & reinforcement allowance | 15% | Editable assumption; set from your shop's fabrication records |
| Prices | Blank | Enter your material and shop $/lb |
Assign gauge after you take off size.
Duct gauge depends on the duct's largest dimension and the pressure class in the mechanical specification, usually referencing SMACNA construction standards. Take off duct by size and run first, then assign the gauge each size requires. Assigning one gauge to the whole job either overprices small branches or underprices the trunks.
From calculator to bid: get the quantities off the drawings.
Speed is easy to promise. Defensible numbers are the job, so RenderDraw keeps the estimator in control of every quantity that gets priced.
- Source on every row. Each quantity keeps its source sheet, location and reviewer decision.
- Lowest confidence first. The review queue shows the drawing tile with the detection highlighted and the extracted value.
- Uncertain items flagged, not hidden. Anything the AI can't confirm goes to the estimator rather than being guessed.
- Nothing priced before approval. Rows move on to pricing only after they are accepted.
Questions estimators ask
How do you calculate the weight of ductwork?
Find the surface area of sheet (perimeter × length for rectangular, π × diameter × length for round), multiply by the weight per square foot for the gauge, and add an allowance for seams, joints and reinforcement.
How much does 26 gauge galvanized weigh?
About 0.906 lb per square foot, per published galvanized gauge tables. 24 gauge is about 1.156 and 22 gauge about 1.406 lb per square foot.
What is sheet metal price per foot?
It depends on size, gauge and your $/lb, so the calculator derives it: weight per foot × price per pound. A 24 × 12 duct in 22 gauge is about 8.4 lb/ft before allowance.
Should I price duct by weight or by foot?
Many mechanical contractors price fabricated duct by weight because material and shop labor scale with pounds. Price per foot is a useful check for each size.
Can AI take off ductwork?
Yes, with review. RenderDraw proposes duct runs by size from the mechanical plans, linked to the source sheet, for your estimator to approve before gauge and pricing are applied.
See what the AI reads on your own drawings.
Send one representative HVAC plan set. RenderDraw reviews it and follows up with what the AI extracted and what it flagged for review. Your files remain private while the request is assessed, and there is no obligation.
- Upload mechanical plans, equipment and air device schedules, duct sections, controls drawings and the Division 23 spec sections.
- RenderDraw reviews the set and the scope you want tested.
- We follow up with extracted quantities, flagged items and next steps.