How Thick Is 18-Gauge Sheet Metal?

A material's gauge is often considered to be the thickness of the material. Metal objects, including wire, sheet metal, tubing and hypodermic needles, are categorized by their gauges. Sheet metal gauges are not universally standardized. Depending on the gauge system used to classify the material and the composition of the material, two sheets of metal with the same thickness may have different gauges.

Continuous sheet of metallic material being fed through machine
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A close-up of sheet metal being passed through a machine.

Common Gauge Measurement Systems

Three common systems of measurement are used to classify the gauge of metal products. The Brown and Sharp Gauge, also known as the American Wire Gauge, is used for metals such as aluminum and brass. The Manufacturers Standard Gauge measures the thickness of the most common types of steel used in manufacturing, including traditional steel, stainless steel and galvanized steel. The Birmingham Gauge, primarily used in the United Kingdom, is used to measure a variety of metals, especially those made into strips or tubing.

Factors That Determine the Gauge of Sheet Metal

When you compare two sheets of compositionally identical metal, their gauges are based on the thicknesses of the sheets. Conversely, two sheets of metal with the same thickness but different compositions may classified as having different gauges. Depending on the gauge system used by the manufacturer, the sheet metal gauge may also consider factors such as the weight in pounds of 1 square foot of the sheeting material and the material's tensile strength.

Sheet Metal Gauge Charts in the U.S.

The Manufacturers Standard Gauge, most commonly used in the U.S., evolved from the U.S. Standard Gauge, which was developed in 1893. The U.S. standard creates relative uniformity among sheet metal manufacturers and purveyors. The standardized gauge allows sheet metal consumers to know, within a small range of error, the properties — weight, thickness and gauge — of the material being purchased.

Thickness of 18-Gauge Sheet Metal

Using the Manufacturers Standard Gauge table, the thickness of 18-gauge mild steel sheet metal is .0478 inch thick. The thickness of an 18-gauge aluminum sheet is .0403 inch. The thickness of an 18-gauge stainless steel sheet is .0516 inch.