Approximate Ring Size Converter
Convert a US, EU circumference or Japan reference into a simplified US/UK/EU/Japan crosswalk.
Last updated · View algorithm, constants and default inputs (JSON)
US
About this calculator
This calculator uses one simplified circumference model to estimate US, UK, EU and Japan labels. Ring systems use different conventions, and this model is not a universal standard. ISO 8653:2016 specifies how ring size is measured and designated; it does not make every retail conversion identical. Confirm with the jeweler or maker.
Choose the calculation that matches your task
Use this converter when the starting input is a regional ring-size label. It estimates equivalent labels and dimensions using a simplified model. If your input is a measured circumference or diameter, the measurement estimator provides that input path and a fit adjustment.
Worked example
calculated with the default values below
Your ring size system US · Size in selected system 7 US 7 · UK N · EU / ISO 54 · Japan 14 · Inside diameter 17.3 mm · Inside circumference 54.4 mm
General background references
Disclaimer
These calculators give general estimates. Sizing, pricing, availability and standards vary by brand, retailer and country, so treat the output as a starting point and confirm it against the seller's or authority's own figures.
Implementation source
This record describes the implementation used by this page. It is not independent validation. External references, when available, support only the stated formula or definition; estimates and custom rules retain their own assumptions.
Formula and variables
C_US = 44.2 + (US − 3)×2.55; C_EU = EU; C_JP = (JP÷3 + 12.67)×π; d = C÷π
- C
- Estimated inside circumference (mm)
- d
- Estimated inside diameter (mm)
- US/EU/JP
- Selected sizing reference
Selected source scale is converted to an estimated circumference. The model rounds US to half sizes, derives UK/EU/Japan labels and is approximate; retail charts may differ.
Frequently asked questions
How does the ring-size crosswalk work?
The calculator maps the selected US, EU circumference or Japan reference to an estimated inside circumference, rounds to a US half size, then derives the other labels. ISO 8653:2016 specifies measurement and designation, while retail charts may still differ; confirm with the jeweler or maker.