完全無料 • アプリ不要

あなたの指輪の号数を、今すぐ測定。

最も正確なオンラインリングサイズ測定ツール。カードや定規で画面を調整し、日本サイズ(号数)、US、UK、EUサイズを判定。

100% 端末内で処理
Auto-Detect • カードで調整 • 硬貨で調整
15+ Countries
完全無料 • アプリ不要

ステップ1: 画面のキャリブレーション

クレジットカード、硬貨、または定規を画面の枠に合わせて1:1の原寸大に設定します。

リングサイズ国際換算表

日本の号数(1号〜30号)、内径、円周、US、UK、ヨーロッパ規格の比較一覧表。

Essential Measurement Anatomy

Inside Diameter vs. Inside Circumference

Understanding the difference is critical to avoid sizing errors. All international ring size charts are built on these two core measurements.

1Straight Measurement
d (mm)

Inside Diameter

The straight-line distance across the widest point inside the ring opening.

DIAMETER (d)
How to measure: Measure from the inside edge across the widest center to the opposite inside edge.
Best for: Measuring an existing ring that already fits you perfectly.
Never measure the outer rim: Ring thickness adds 2–4 mm, causing an error of 3 to 5 whole sizes!
2Perimeter Measurement
C = π × d (mm)

Inside Circumference

The complete continuous distance around the inside inner wall of the ring.

CIRCUMFERENCE (C)
How to measure: Wrap string or paper strip snugly around your finger base, mark the overlap, and measure length.
ISO Standard: European (EU) sizes correspond 1:1 with inside circumference in mm (e.g. 54 mm = EU 54).
Direct Finger Fit: Inside circumference exactly mirrors the perimeter of your finger tissue for 100% true comfort.
π

The Exact Mathematical Relationship

Circumference = Diameter × 3.14159 • (or Diameter = Circumference ÷ π)

Example: 17.3 mm (d) × π = 54.4 mm (C) = US Size 7
ISO / 欧州内径 (mm)US / カナダUK / 英国インド日本 (号数)
4915.7 mm5J99
5216.5 mm6L1212
5417.3 mm7N1414
5718.1 mm8P1716
5918.9 mm9R1918
6219.8 mm10T2220
6520.6 mm11V2423
6721.4 mm12X2625
Frequently Asked Questions

リングサイズに関するFAQ

画面キャリブレーションの仕組みやサイズの選び方に関するアドバイス。

Need more ring sizing help?

Explore our interactive tools, calculators, and printable size guides anytime.