Duct Weight Calculator (SMACNA Gauge & Pounds)
Enter a duct size and length and get the galvanized sheet metal weight in pounds — with the SMACNA minimum gauge selected automatically from the size, or your own gauge if the spec states one. These are the same gauge and lb/ft² tables DuctIQ's takeoff engine and bid-sheet export use, so the number here matches what a full takeoff would compute for the same run.
Enter duct size and length to calculate.
How the weight is calculated
Duct weight is surface area times sheet weight. The perimeter of the duct in inches (2 × (W + H) for rectangular, π × diameter for round) divided by 12 gives feet of metal per foot of run; multiplied by the length it gives total square feet; multiplied by the gauge's lb/ft² it gives pounds. A 24" × 12" rectangular run at 24 ga is 6 ft² of metal per linear foot × 1.156 lb/ft² ≈ 6.9 lb per foot — 100 LF is roughly 694 lb of raw metal before seam and waste allowances.
SMACNA minimum gauge and galvanized weight tables
Rectangular duct (largest side)
| Largest side | SMACNA min gauge | Galvanized weight |
|---|---|---|
| up to 12" | 26 ga | 0.906 lb/ft² |
| 13–30" | 24 ga | 1.156 lb/ft² |
| 31–54" | 22 ga | 1.406 lb/ft² |
| 55–84" | 20 ga | 1.656 lb/ft² |
| over 84" | 18 ga | 2.156 lb/ft² |
Round / spiral duct (diameter)
| Diameter | SMACNA min gauge | Galvanized weight |
|---|---|---|
| up to 14" dia | 26 ga | 0.906 lb/ft² |
| 15–26" dia | 24 ga | 1.156 lb/ft² |
| 27–36" dia | 22 ga | 1.406 lb/ft² |
| 37–50" dia | 20 ga | 1.656 lb/ft² |
| over 50" dia | 18 ga | 2.156 lb/ft² |
Low-pressure (±½" w.g.) galvanized minimums from the SMACNA HVAC Duct Construction Standards, before reinforcement-based adjustments. G90 galvanized sheet weights include coating. A stated project spec or higher pressure class always governs.
From one run to a whole drawing set
This calculator answers one run at a time — useful for a spot check or a hanger calc. A bid needs every run: sizes and lengths measured from the plan, gauge resolved per run from the spec or the SMACNA minimum, and the pounds rolled up by system. That measuring step is what DuctIQ automates: upload the mechanical PDF and it returns every duct run as a reviewable line item with size, length, gauge, and weight, exported to Excel/CSV with sheet metal totals — using the same tables as this page.
Run a free takeoff on your drawingDownload a sample takeoff (Excel)
Frequently asked questions
How do you calculate the weight of sheet metal duct?
Surface area times sheet weight: perimeter (in inches) ÷ 12 × length in feet gives square feet of metal, multiplied by the gauge's weight in lb/ft² (galvanized 26 ga ≈ 0.906, 24 ga ≈ 1.156, 22 ga ≈ 1.406, 20 ga ≈ 1.656, 18 ga ≈ 2.156, 16 ga ≈ 2.656). For round duct the perimeter is π × diameter. This calculator does exactly that, and picks the SMACNA minimum gauge from the duct size when you don't specify one.
What gauge does SMACNA require for my duct size?
For low-pressure (½" w.g.) galvanized rectangular duct, the SMACNA minimums by largest side are: up to 12" → 26 ga, 13–30" → 24 ga, 31–54" → 22 ga, 55–84" → 20 ga, larger → 18 ga. Round/spiral runs lighter: up to 14" dia → 26 ga, to 26" → 24 ga, to 36" → 22 ga, to 50" → 20 ga, larger → 18 ga. A higher pressure class or a project spec always overrides these minimums — check your spec first.
Does the calculated weight include seams, joints, and waste?
No — it is the geometric metal weight only (surface area × lb/ft²), which is also how DuctIQ's bid sheet documents raw metal. Shops typically add their own allowance for seams, connectors, reinforcement, and waste, commonly in the 10–25% range depending on fabrication method; apply your factor on top so the assumption stays visible in your estimate.
Why does duct weight matter for an HVAC bid?
Sheet metal is often priced per pound: total pounds drive material cost, shop labour is frequently estimated per pound fabricated, and hanger/support design depends on weight per foot. Getting from a drawing to accurate pounds means measuring every run's size and length first — which is exactly the takeoff step DuctIQ automates from the mechanical PDF.
Can I get duct weights for a whole drawing set automatically?
Yes — that is what DuctIQ does. Upload the mechanical PDF and it measures every duct run, assigns gauge (from your spec when stated, SMACNA minimum labelled as such when not), and exports Excel/CSV with per-line and total sheet metal weights using the same tables as this calculator. The first takeoff is free.
Stop measuring runs one at a time
DuctIQ reads the mechanical drawing, measures every duct run, assigns gauge, and totals the pounds — reviewable line by line, exported to Excel. First takeoff free.
Start your free takeoffSee pricing & plans