Ring Size Converter
Start with a known size or an inner measurement. See approximate equivalents across four sizing systems.
Sizes are approximate and use the GIA reference chart. EU here means the inner circumference in millimeters, rounded to the nearest whole size; it is not the Swiss sizing system. JP results use the Japan entries in the chart. Brands and gauges may differ.
For custom manufacturing, confirm the finished inner diameter, tolerance, band width and approved sample with your supplier. This converter does not determine finger fit or compensate for wide bands.
View reference chart & method
US and UK values are looked up from the chart, not generated with a linear formula. Measurements use C = π × D. Each result independently selects the nearest available reference size; an exact halfway value selects the larger size. Results outside a system's reference range show “Outside chart”. Dimensions in the source are rounded to 0.1 mm.
Reference: GIA — International Ring Size Chart. Supported US range: 3–12.5; UK: F–Y; JP: 4–26. EU and measurement inputs cover the same diameter range, 14.1–21.8 mm.
| US | UK | EU ≈ | JP | Inner Ø mm | Inner C mm |
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