Ring Size Converter
Convert ring sizes between US, UK (letters), EU/ISO 8653 and Japan/China systems. Get inner diameter and circumference in mm. Free online, no upload.
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What is Ring Size Converter?
The Ring Size Converter is a free online tool that translates a ring measurement between the US, UK, EU/ISO 8653 and Japan/China sizing systems. Enter a size in any one system and the tool immediately shows the equivalent values in all the others, plus the inner circumference and inner diameter in millimetres. UK half-letter sizes (N, N½, O½) are supported alongside numeric sizes, and you can copy the full set of equivalents to the clipboard in a single click. Everything runs locally in your browser with no uploads, so it is safe to use for gifts, engagement rings and online jewellery shopping.
Key Benefits
- Convert instantly between four international ring sizing standards
- Accepts UK half-letter sizes as well as plain numbers
- Shows inner circumference and diameter in mm for direct measurement
- Copy every equivalent size to the clipboard in one click
- Fully client-side and offline-capable — no data leaves your device
Common Use Cases
- •Online jewellery shopping: translate a US size from an American store into your local EU or JP size
- •Engagement and wedding rings: confirm the partner's size across systems before ordering abroad
- •Gift giving: convert a size you know into the system the recipient's jeweller uses
- •Ring making and resizing: use the inner circumference and diameter to measure a band or a finger directly
- •International travel: quickly find your ring size in the local standard
How to Use the Ring Size Converter
- Choose a System: Pick the sizing system you already know — US, UK (letters), EU/ISO, or Japan/China — from the dropdown.
- Enter Your Size: Type the ring size value. For UK, enter the letter (N, N½, O½). For the others, enter the numeric size.
- Read the Equivalents: The results panel shows the matching US, UK, EU/ISO and JP sizes, plus inner circumference and inner diameter in mm.
- Copy and Confirm: Click "Copy all sizes" to save every equivalent to the clipboard. Confirm the final size with your jeweller before ordering.
Key Features
- Bidirectional conversion across US, UK (letters), EU/ISO 8653 and Japan/China systems.
- Accepts UK half-letter sizes (N, N½, O½) as well as numeric sizes.
- Reports inner circumference and inner diameter in millimetres for direct measurement.
- Copy all equivalent sizes to the clipboard in one click.
- 100% client-side — no data leaves your device, works fully offline.