18 gauge steel has a thickness of approximately 0.0478 inches (about 1.214 millimeters)

. This thickness is specific to steel; other metals like aluminum have different thicknesses at the same gauge number (for example, 18 gauge aluminum is about 0.0403 inches thick)

. The gauge system does not correspond directly to a fixed unit of measurement but is standardized for each metal type, with 18 gauge steel consistently around 0.0478 inches thick