Ring Size Converter
Convert ring sizes between US, EU, diameter, and circumference measurements.
Convert ring sizes instantly. Free US, EU, UK and Japan ring size converter with inner diameter and circumference.
Calculator Inputs
About Ring Sizes
Convert ring sizes between US, EU, diameter, and circumference measurements.
Ring systems all describe the inner circle. The US scale is linear in diameter (about 0.81 mm per size from an 11.63 mm zero), and the EU ISO scale is simply the inner circumference in millimeters. Enter any one measurement to get the other three.
Wide bands fit tighter than thin ones — most jewelers suggest a quarter to half size up above 6 mm width. Finger size also shifts with temperature and time of day; measure in the evening. Everything runs in your browser.
Where it is used
Ordering rings from international sellers, converting heirloom sizes, and checking printable ring sizers.
How to use the Ring Sizes
- Size Value — enter the value (e.g. 6).
- Size System — enter the value.
- Calculate — press the Calculate button to see the result instantly above.
Formula
US diameter ≈ 11.63 + 0.8128×size mm. EU (ISO 8653) = inner circumference in mm.
Examples
Example
Frequently Asked Questions
- Why do charts disagree by half a size?
- Manufacturing tolerance plus rounding between systems. Half-size disagreement is normal; diameter in millimeters is the unambiguous truth.
- Should wide bands size up?
- Yes, typically a quarter to half size. More metal covering the finger means more squeeze at the same diameter.
- When should I measure my finger?
- Evening, at room temperature, when fingers are largest. Cold mornings can read a half size small.