Ring size
tools for measuring sizes of rings and fingers
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, aluminum, alongside digital variants and web-based ring sizer applications.
Measurement systems
International standard
ISO 8653:2016 defines standard ring sizes in terms of the inner circumference of the ring measured in millimeters. ISO sizes are used in Austria, France, Belgium, Nordic countries (Norway, Sweden, Denmark, Finland, Iceland), and other countries in Continental Europe.
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 1⁄4 steps, where whole sizes differ by 0.032 inches (0.81 mm) of internal diameter, equivalent to 0.1005 inches (2.55 mm) of internal circumference. The relationship of this size (
s
N
A
{\displaystyle s_{NA}}
) to ISO 8653:2016 circumference (
C
I
S
O
{\displaystyle C_{ISO}}
) is
C
I
S
O
=
2.55
×
s
N
A
+
36.5
{\displaystyle C_{ISO}=2.55\times s_{NA}+36.5}
, while the relationship to ISO 8653:2016 diameter (
d
I
S
O
{\displaystyle d_{ISO}}
) is
d
I
S
O
=
0.8128
×
s
N
A
+
11.63
{\displaystyle d_{ISO}=0.8128\times s_{NA}+11.63}
.
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.
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