In Australian commercial construction projects, the term "nominal size" refers to the standard or typical size of a building component, material, or system, as opposed to its actual or precise dimensions. Nominal sizes are used for convenience and consistency in design, specification, and procurement.

For example, the nominal size of a timber stud in a wall frame is usually 90mm x 45mm, which means the stud has a width of 90mm and a height of 45mm. However, the actual dimensions of the stud may be slightly different due to manufacturing tolerances and variations in wood species and moisture content.

Similarly, the nominal size of a steel beam may be 150mm x 150mm, which means the beam has a width and height of 150mm each. However, the actual dimensions of the beam may be slightly larger or smaller depending on the steel grade, section shape, and fabrication process.

Nominal sizes are also used for other building components such as concrete slabs, bricks, blocks, pipes, cables, and fixtures. They help to simplify communication and coordination between architects, engineers, contractors, and suppliers, and to ensure that the components fit together properly and meet the required performance criteria.