IEC 60228 is the International Electrotechnical Commission (IEC)'s international standard on conductors of insulated cables. As of 2023 the current version is Third Edition 2004-11Among other things, it defines a set of standard wire cross-sectional areas:
In engineering applications, it is often most convenient to describe a wire in terms of its cross-section area, rather than its diameter, because the cross section is directly proportional to its strength and weight, and inversely proportional to its resistance. The cross-sectional area is also related to the maximum current that a metallic wire can carry safely.