About the Sheet Metal Gauge Converter
This sheet metal gauge converter turns a gauge number into actual thickness in inches and millimetres, and works in reverse to find the nearest gauge for a measured thickness. It covers uncoated steel, galvanized steel, aluminum and stainless steel, and also estimates the weight of the sheet per square foot. A full gauge chart for the chosen material is shown below the result.
Gauge is not a unit of length, and the same gauge number means a different thickness depending on the metal. Uncoated steel follows the Manufacturers’ Standard Gauge, galvanized sheet is slightly thicker to allow for the zinc coating, aluminum is normally specified by the Brown & Sharpe (AWG) system, and stainless is often quoted using the older US Standard Gauge. For example, 16 gauge is 0.0598 in in steel but only 0.0508 in in aluminum.
Use it when reading HVAC duct, roofing, flashing, enclosure or fabrication drawings, or when ordering sheet stock. Mills allow a thickness tolerance around each nominal value, and many suppliers now quote decimal thickness directly, so confirm the decimal figure when it matters.
How to use the sheet metal gauge converter
- 1Choose whether to convert a gauge to thickness or a thickness to a gauge.
- 2Select the material, since each metal uses a different gauge system.
- 3Enter the gauge number, or the measured thickness in mm or inches.
- 4Read the thickness in inches and mm, or the nearest gauge.
- 5Check the chart below for neighbouring gauges and weights.
Formula and method
Steel, galvanized and stainless gauges are lookup tables rather than a formula, because the systems were originally defined by weight per square foot. The converter looks up the nominal decimal thickness for the gauge and material and multiplies by 25.4 to convert inches to millimetres. In reverse, it picks the gauge whose nominal thickness is closest to the value you measured.
Aluminum follows the Brown & Sharpe (AWG) system, which is geometric: each gauge step changes the thickness by a factor of about 1.123, from 0.46 in at 0000 gauge to 0.005 in at 36 gauge. Weight is thickness × 144 square inches × density, using about 0.2836 lb/in³ for steel, 0.289 for stainless and 0.0975 for aluminum; zinc coating weight is ignored for galvanized sheet.
- G
- Gauge number
- d
- Thickness (in)
- density
- Metal density (lb per cubic inch)
Worked examples
16 gauge steel
In the Manufacturers’ Standard Gauge, 16 gauge is 0.0598 in, which is 0.0598 × 25.4 = 1.519 mm. At 0.2836 lb/in³ it weighs about 2.44 lb per square foot.
20 gauge aluminum
Aluminum uses Brown & Sharpe sizes: 0.005 × 92^(16/39) ≈ 0.0320 in, or 0.813 mm — much thinner than 20 gauge steel at 0.0359 in. It weighs only about 0.45 lb per square foot.
Which gauge is 1.2 mm galvanized?
1.2 mm is 0.0472 in. The closest galvanized gauges are 19 (0.0456 in) and 18 (0.0516 in); 19 gauge is nearer, about 0.04 mm thinner than measured.
18 gauge stainless
The US Standard Gauge used for stainless sets 18 gauge at 0.050 in, or 1.27 mm, weighing about 2.08 lb per square foot.
Frequently asked questions
How thick is 16 gauge steel?+
16 gauge uncoated steel is 0.0598 in (1.52 mm). Galvanized 16 gauge is 0.0635 in (1.61 mm), 16 gauge stainless is 0.0625 in (1.59 mm) and 16 gauge aluminum is 0.0508 in (1.29 mm).
Why does a higher gauge mean thinner metal?+
Gauge numbers grew out of wire drawing, where each additional pass through a die made the wire thinner and the count went up. Sheet gauges kept the convention, so 10 gauge is much thicker than 26 gauge.
Is aluminum gauge the same as steel gauge?+
No. Aluminum is sized with the Brown & Sharpe (AWG) system, so the same number is thinner than in steel: 18 gauge aluminum is 0.0403 in, while 18 gauge steel is 0.0478 in. Always confirm the decimal thickness when ordering.
What gauge is used for HVAC ductwork and roofing?+
Residential galvanized duct is usually 30 to 26 gauge, with the minimum set by duct size and whether the duct is exposed in the IRC and SMACNA tables; commercial duct is often heavier. Metal roofing panels are typically 29, 26 or 24 gauge, with 24 being the heaviest common residential choice.
How do I measure sheet metal gauge?+
Measure the thickness with calipers or a micrometer away from any burr or coating damage, then use the thickness mode to find the nearest gauge for that material. A notched sheet metal gauge tool also works for quick checks.