How to Convert Gauge Duct to Thickness in Inches

Written by joshua smyth
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How to Convert Gauge Duct to Thickness in Inches
The metal used for ventilation ducts has a gauge number to indicate its thickness. (ventilation ducts image by Ragne Kabanova from

The thickness of the metal used for ductwork is typically described with a "gauge" number that can be a bit frustrating to translate into real-life measurements. Gauges are inversely related to the thickness of the metal, meaning that larger gauges are attached to thinner pieces of sheet metal. Gauges also attach to slightly different thicknesses for different types of metal. To convert a duct's gauge to its thickness in inches, you need to use a conversion chart that lists the thicknesses of the different types of steel and aluminium.

Skill level:

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Things you need

  • Calipers
  • Conversion chart

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  1. 1

    Look up the gauge of the metal used in the ducts you are attempting to convert. Some manufacturers stamp it into the metal on each piece. If you can't find the gauge, do the calculation in reverse by measuring the thickness of the duct in inches using a pair of calipers.

  2. 2

    Determine what material the duct is made out of. Gauges describe slightly different thicknesses of sheet steel, galvanised steel, stainless steel and aluminium. Ductwork used for forced-air heating and cooling can be made of any of these materials. There is also a U.S. standard thickness that serves as an average associated with that gauge.

  3. 3

    Locate the gauge number in the leftmost column conversion chart.

  4. 4

    Look at the columns to the right of the gauge number for the thickness in inches for each different metal. For example, a piece of 16 gauge metal has a U.S. standard thickness of 0.0625 inch, 0.0598 inch for sheet steel, 0.064 inch for galvanised steel, 0.0625 inches for stainless steel and 0.0508 inch for aluminium.

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