It’s confusing to many people that steel cable, rod and sheet stock are measured using a system that appears counter-intuitive. As conventional measurements increase in number, so does weight and thickness, right? In fact, not right! The thickness of metal cable, rod and sheet stock is measured in gauge, and gauge refers back to a system in which the physical properties actually decrease as the rating number increases.

It’s uncommon knowledge! Few people know why the thickness of steel diminishes as the gauge increases (ie: 16 gauge steel is thicker than 20 gauge steel). The explanation comes from the early development of a steel gauge measurement system in which the control measurement was based on a 1″ thick steel plate. The 1″ thickness of the steel was measured in diminishing fractions such as 1/14″ thick, 1/16″ thick, 1/20″ thick, and so on. The bottom number of the fraction became an easy identifier and eventually was adopted as the “gauge number.” Thus, 1/16″ became 16 gauge and 1/20″ became 20 gauge. The concept makes sense but without explanation, the converse number is often confusing. By taking the gauge number and returning it back to a fractional format, one can discover the actual nominal thickness dimension, in inches, of sheet steel.

Your statement ” By taking the gauge number and returning it back to a fractional format, one can discover the actual nominal thickness dimension, in inches, of sheet steel.” is not correct. The actual thickness of the sheet metal is not 1 divided by the gauge number. For 20 gauge your formula is 1/20 = 0.05 for the thickness, however, 20 gauge sheet is actually 0.0359″. Your formula does clear up which gauge is larger, but isn’t accurate for the true thickness of the sheet metal.

HI Lloyd,

Thank you for your comments about gauge, so many people believe that the larger the number, the thicker the steel. I am glad that the explanation was helpful. As to the measurement, in commercial steel, there is an acceptable gauge range and both measurements are within the tolerance.

Many thanks,

Howard

Who care about the actual thickness of the sheet metal ! Only gauge 15 is the correct formula is 1/15 = 0.067″. You are right: 1/20 gauge should be 0.05 but it is 0.036″, 10 gauge should be 1/10 = 0.1 but is 0.135″. Again only 15 gauge is the correct formula, smaller number than 15 gauge must be add up a fraction number, the bigger number than 15 gauge must be minus a fraction number, who know someone may invent another pi “π” in the future, if you check another website will be different a little bit for all numbers (http://www.metaltrone.com/metalgauge-chart.pdf).

The main meaning is the bigger gauge number is the smaller thickness, the smaller gauge number is the bigger thickness. Simply 20 gauge is smaller than 15 gauge.

Thank you Howard “… there is an acceptable gauge range and both measurements are within the tolerance”.

Linh

Thank you Linh, I am glad you agree with this article. It is confusing for many people.

Stay safe!

With thanks,

Howard