Insights · Reference
Duct drawings talk in gauge; machines are rated in millimetres. This reference converts sheet metal gauge to millimetres and inches for galvanised duct steel, then shows which Taokron duct machine forms each gauge — with the machine thickness ranges taken verbatim from the Taokron Product Catalog 2026.
Sheet metal gauge is an older imperial system: the higher the number, the thinner the metal. It is not linear, and the thickness a gauge number represents differs between galvanised steel, stainless and aluminium. The table below is the Galvanized Steel Sheet Gauge standard — the one that applies to the galvanised coil most HVAC duct is built from — with nominal inch and millimetre equivalents and where each gauge typically lands in duct work.
| Gauge (GSG) | Nominal inch | Nominal mm | Typical duct use |
|---|---|---|---|
| 30 | 0.0157″ | 0.40 mm | Light flexible-duct collars, lightest fittings |
| 28 | 0.0187″ | 0.48 mm | Light round duct and fittings |
| 26 | 0.0217″ | 0.55 mm | Small low-pressure duct — the common light gauge |
| 24 | 0.0276″ | 0.70 mm | General low-pressure rectangular and round duct |
| 22 | 0.0336″ | 0.85 mm | Mid-size duct, higher pressure |
| 20 | 0.0396″ | 1.01 mm | Large duct, medium/high pressure |
| 18 | 0.0516″ | 1.31 mm | Large/high-pressure duct, plenums, heavy fittings |
| 16 | 0.0635″ | 1.61 mm | Industrial duct, dust/fume, heavy plenum |
| 14 | 0.0785″ | 1.99 mm | Heavy industrial, abrasion-handling duct |
| 12 | 0.1084″ | 2.75 mm | Plate work — cut, not roll-formed as duct |
Gauge values follow the Galvanized Steel Sheet Gauge standard and are nominal coated thicknesses — confirm against your material certificate. Stainless steel and aluminium use different gauge-to-thickness scales; when in doubt, specify in millimetres.
Quick convert
Pick a gauge or type a thickness.
Nominal galvanised coated thicknesses (GSG standard). Stainless and aluminium use different scales — specify in mm.
More free Taokron tools: Machine selector · Payback & ROI calculator · Duct weight estimator
The next table is the other half of the answer: the thickness range each Taokron duct-forming machine actually handles, in galvanised, stainless and aluminium, taken verbatim from the Product Catalog 2026. Read it against the chart above to match a gauge to a machine.
| Machine | Model | Galvanised | Stainless | Aluminium |
|---|---|---|---|---|
| Spiral tubeformer (round duct) | SBTF-1500 | 0.4–1.2 mm | 0.4–0.8 mm | — |
| SBTF-1500C | 0.4–2.0 mm | 0.4–1.2 mm | — | |
| SBTF-1602 | 0.4–1.3 mm | 0.4–0.8 mm | 0.4–1.3 mm | |
| SBTF-2020 | 0.4–2.0 mm | 0.4–1.2 mm | 0.4–2.0 mm | |
| Auto duct line (rectangular) | SBAL-V | 0.5–1.5 mm | 0.5–1.5 mm | — |
| SBAL-III | 0.5–2.0 mm | 0.5–2.0 mm | — | |
| SBAL-II | 0.5–2.0 mm | 0.5–2.0 mm | — |
Source: Taokron Product Catalog 2026, manufacturer nameplate specifications. Spiral tubeformers form round duct Φ80–Φ2500 mm; auto duct lines form rectangular TDF duct up to 1550 mm wide. Full per-model figures: spiral comparison and auto line comparison.
30–20 gauge (0.40–1.0 mm). The everyday HVAC range. Every Taokron spiral tubeformer and every auto duct line forms it — they all run down to 0.4–0.5 mm. If your work is standard low-pressure galvanised duct, any model in the range covers it.
18 gauge (≈1.3 mm). Above 1.2 mm you narrow the field. In round duct that means the SBTF-1602 or SBTF-2020 (galvanised to 2.0 mm); in rectangular, the SBAL-V (to 1.5 mm). The lighter SBTF-1500/1500C and SBAL-III/II top out at 1.2 mm.
16–14 gauge (≈1.6–2.0 mm). Heavy-gauge galvanised round duct is the SBTF-1602 / SBTF-2020 territory (0.4–2.0 mm). For seam-welding that gauge, the SBFN-100 seam welder reaches 2.0 mm and the medium-frequency welder reaches 3.0 mm in stainless or carbon steel.
12 gauge and heavier (2.75 mm+). This is plate, not roll-formed duct. You cut it rather than form it: shearing handles 2–4 mm, plasma and laser to 8 mm. Aluminium is the exception — the SBTF-1602/2020 roll aluminium to 2.0 mm.
Gauge selection is set by duct size and pressure class, not preference. As a working rule of thumb for low-pressure rectangular duct:
Treat this as orientation, not specification. Always confirm the required gauge against SMACNA HVAC Duct Construction Standards or AS/NZS 4254 for your exact size, pressure class and reinforcement — the standard, not the rule of thumb, governs the job.
Tell us your gauge and duct type for a machine recommendation →
24 gauge galvanised steel is a nominal 0.70 mm (0.0276″). It is one of the most common HVAC duct gauges, and every Taokron spiral tubeformer and auto duct line forms it — they all run down to 0.4–0.5 mm.
In galvanised steel, roughly 30 to 14 gauge (0.4–2.0 mm). the SBTF-1602 forms 0.4–1.3 mm (galvanised and aluminium) and the SBTF-2020 0.4–2.0 mm; SBTF-1500 forms 0.4–1.2 mm and SBTF-1500C 0.4–2.0 mm; SBAL-V forms 0.5–1.5 mm; SBAL-III/II form 0.5–2.0 mm. For plate over 2 mm, shearing, plasma and laser cut up to 8 mm.
Gauge is an older imperial scale where a higher number means thinner metal (26 ga is thinner than 20 ga). Millimetres measure thickness directly. The two are not linear, and the gauge-to-mm value differs by material, so convert with the correct standard. Taokron catalogue figures are in millimetres.
Most low-pressure duct is 26 to 20 gauge (0.55–1.0 mm), increasing with duct size and pressure. Small low-pressure duct uses 26 gauge; large or higher-pressure duct uses 22–18 gauge. Confirm against SMACNA or AS/NZS 4254 for your pressure class.
Low-pressure rectangular duct is mostly 26 to 24 gauge (0.55–0.70 mm) galvanised, stepping up to 22 to 20 gauge (0.85–1.0 mm) on larger sections and higher pressure per SMACNA and AS/NZS 4254. Taokron machines form 0.4 mm up to 2.0 mm, covering the full HVAC range.
It depends on the machine. The light-gauge spiral tubeformers SBTF-1500 and SBTF-1602 run 0.4–1.3 mm; the heavier SBTF-1500C and SBTF-2020 reach 2.0 mm, and the SBAL auto duct lines form 0.5–2.0 mm. Match the machine to your heaviest planned gauge.
Tell us the gauge and duct type you build and an Taokron engineer will tell you which machine forms it — within 12 hours, and not a salesperson.
Ask an engineerThe duct fabrication workflows above run on standard Taokron equipment: spiral tubeformers for round duct, auto duct production lines for rectangular duct, and TDF flange and lockformer machines for closure — or browse the full machine catalog.
