The "W" stands for "Wide Flange," which is the modern, prevalent type of structural H-beam. The designation "W12x30" provides the nominal dimensions:
"W": Indicates the shape is a wide-flange beam with essentially parallel flange surfaces.
"12": The nominal depth of the beam in inches (approximately 12 inches from the outer face of the top flange to the outer face of the bottom flange).
"30": The weight of the beam in pounds per linear foot.
Therefore, a W12x30 is a wide-flange beam about 12 inches deep that weighs 30 pounds per foot. This designation system, established by the American Institute of Steel Construction (AISC), allows for easy selection from standard tables that list the exact dimensions (depth, flange width, flange thickness, web thickness) and engineering properties (moment of inertia, section modulus) for each size. An A36 H-beam will be ordered and detailed using this "W-shape" nomenclature.