FitMyRing / Guide
Ring-size conversions: why charts can disagree
International labels are derived from diameter or circumference, but rounding and local conventions can change the answer.
US, UK, European, Japanese, and other ring systems do not share one label format. A conversion chart maps the same physical ring to different numbers or letters, often with rounding between available sizes.
KEY POINTS
- Inner diameter in millimetres is a more portable reference than a regional label.
- A conversion may land between two sizes because each system uses different increments.
- Band width, shape, and manufacturer tolerance still affect the final fit.
Start from a physical measurement
A useful chart begins with inner diameter or inner circumference. If two charts show different converted labels, compare the millimetre values behind them before choosing a size.
Understand rounding
Some systems offer half sizes, some use letters, and others track circumference more directly. The measured value may sit between stock sizes, so a chart must round up or down according to its own rule.
Ask how the ring is made
A wide band, comfort-fit interior, unusual material, or custom setting can change the recommended size. When ordering from a specific maker, use that maker’s chart and share the measured diameter for context.
Sources and further reading
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