Ring size is a measurement used to denote the circumference (or sometimes the diameter) of jewellery rings and smart rings. Measuring tools Ring sizes can be measured physically by a paper, plastic, or metal ring sizer (as a gauge) or by measuring the inner diameter of a ring that already fits. Ring sticks are tools used to measure the inner size of a ring, and are typically made from plastic, delrin, wood, aluminium, or of multiple materials. Digital ring sticks can be used for highly accurate measurements. Measurement systems International standard ISO 8653:2016 defines standard ring sizes in terms of the inner circumference of the ring measured in millimetres. ISO sizes are used in Austria, France, Germany, Belgium, Scandinavia (Norway, Sweden, Denmark, Finland, Iceland), and other countries in Continental Europe. This international standard specifies a method to measure the ring-size using a ring stick with defined characteristics, which is used during manufacturing steps, and specifies the designation of the ring-size. For jeweller-consumer relationships, the finger size is measured with a finger gauge set made up of a ring for each size with the same diameter and tolerance as the ring stick ones. The sizes are in millimeters and correspond directly to the outer circumference of the ring stick to the inner circumference of the finger gauge. Other traditional and regional systems Other ring size measurement systems are used in areas that do not use ISO 8653:2016. North America In the United States, Canada, and Mexico, ring sizes are specified using a numerical scale with steps, where whole sizes differ by of internal diameter, equivalent to of internal circumference. The relationship of this size () to ISO 8653:2016 circumference () is , while the relationship to ISO 8653:2016 diameter () is . The Circular of the Bureau of Standards summarizes the situation with this system: "While there apparently is only one standard in use in the United States, in reality, because of the lack of specific dimensions and because of the errors introduced by the adoption of a common commercial article as a pattern, there are many, although similar, standards." The standards are generally consistent and remain so. There does not appear to have been any improvement in the standard since then. Ireland, United Kingdom, Australia In Ireland, the United Kingdom and Australia, ring sizes are specified using an alphabetical scale with half sizes. Originally in 1945, the divisions were based