Ring Size Calculator
Convert inner circumference or diameter into US/EU ring sizes.
Input Data
System
Size
Results
54
周長 ≈ 54 mm（直徑 17.2 mm）；US≈5.3、EU≈14（近似）。
At a glance:Based on circumference (mm): diameter = circumference ÷ π; US ≈ (circumference − 40.4) ÷ 2.55; EU (French) ≈ circumference − 40. Complements shoe-size and hat-size.
Formula
diameter = circumference ÷ π.
US ≈ (circumference − 40.4) ÷ 2.55.
EU ≈ circumference − 40.
How to Use
- Select the input system and value.
- The tool returns circumference and each size system.
Case Studies
Circumference 54 mm → EU 14, US ≈ 5.3
EU = 54 − 40 = 14; US = (54 − 40.4) ÷ 2.55 ≈ 5.3.
FAQ
Accurate?
Approximate — measure your finger for the best fit.
Use case?
Reference when buying rings.
Precision?
1 decimal.
Related Tools
References
Content review: Calculatorism Science Team. Results are for reference only; please refer to the relevant authorities for the official figures.