指輪サイズ計算機とは？

無料のオンライン指輪サイズ計算機。指の周囲長または直径の採寸から指輪サイズを計算。

Ring sizing is notoriously inconsistent across countries. A US size 7 is a UK size N, an EU size 54, and a Japanese size 14. When buying rings from international jewelers, shopping for engagement rings online, or giving a ring as a gift, getting the correct size is essential. Ring Size Calculator converts between all major sizing systems using circumference, diameter, or a known size.

Choose your input method: measure the circumference of your finger (using a string or paper strip wrapped around your finger and measured in millimeters), measure the diameter of an existing ring that fits (measure the inside edge-to-edge distance), or enter a known size in any system. The calculator immediately shows the equivalent sizes across US, UK, EU, and JP sizing systems.

The complete size chart covers 24 sizes from US 3 to US 15, showing the circumference (in mm), diameter (in mm), and the equivalent size in UK, EU, and JP for each. If your measurement falls between standard sizes, the calculator shows the closest available size with a note about whether it is slightly smaller or larger.

The size chart browser displays all sizes in a clean table format — useful for browsing when you know your size in one system and want to see the full range of equivalents. Standard conversions: US sizes increment by 0.5, UK sizes use letter designations (A-Z), EU sizes use circumference-based numbers, and JP sizes roughly match US but add 10.