Ring Size Converter
Ring sizes are just codes for millimetres: the inside circumference or diameter of the ring. Measure an existing ring or your finger in millimetres, enter the number, and the converter returns your size in the US, UK, EU, and JP systems.
Ring Size Converter
Enter an inner diameter or inner circumference in millimetres to get US, UK, EU and JP ring sizes.
Result
How to measure your ring size at home
- String method: wrap a piece of string or dental floss around the base of the finger. Mark where it meets, then measure the length with a millimetre ruler. That length is the inner circumference.
- Existing ring: lay a ring that fits well flat and measure straight across the inside. That is the inner diameter.
- Measure at the end of the day, when fingers are at their largest, and leave room to get the ring over your knuckle.
- Measure the exact finger you plan to wear the ring on. Sizes differ between fingers and between hands.
- Wide bands fit tighter than thin ones. If you are between sizes for a wide band, consider the larger size.
Mapping follows Daniel Wellington’s published ring size chart (US 4 = UK H = EU 46.5 = JP 7 through US 14 = UK Z+2 = EU 72.3 = JP 27), cross-checked against Norsegarde’s chart with inside diameters and circumferences. EU sizes are the inside circumference in millimetres, rounded. Honest caveats: jewellers’ charts disagree on half-letter and EU half sizes, so a UK O on one chart can be an O 1/2 on another; wide bands and manufacturer tolerances shift the fit. For an expensive ring, confirm with the jeweller’s own chart.
How to use the converter
- Choose how you measured: inner diameter (straight across the inside of an existing ring) or inner circumference (the length around your finger).
- Measure with a millimetre ruler. For the string method, wrap string around the base of the finger, mark where it meets, and measure the string.
- Enter the number and press Convert. The result shows your US, UK, EU, and JP ring sizes.
Understanding your result
The result row gives all four systems at once: US numbers, UK letters, EU as the inner circumference in millimetres, and JP integers. EU is the most literal: EU 46.5 means a 46.5 mm inner circumference. If your measurement falls between two charted sizes, the tool picks the nearest one and says so instead of hiding it.
Measure at the end of the day, when fingers are at their largest, and leave room to get the ring over your knuckle. Wide bands fit tighter than thin ones, so between sizes on a wide band, lean larger.
Worked example
A shopper measures an existing ring: 14.8 mm straight across the inside. They choose inner diameter, enter 14.8, and press Convert. The result: US 4, UK H, EU 46.5, JP 7. The jeweler’s own chart agrees with the row, so they order the US 4 with confidence.
Last reviewed: October 2026.
Frequently asked questions
Is the string method accurate?
It is a good approximation when done carefully: wrap snugly, mark precisely, measure with a millimetre ruler. It can read a half size off if the string stretches or the mark is sloppy. For an expensive ring, measure an existing ring that fits well instead; that is the more accurate route.
Which finger should I measure?
The exact finger you plan to wear the ring on, on the hand you will wear it. Sizes differ between fingers and between hands, sometimes by a full size. A size that fits your right ring finger will not necessarily fit the left.
Why measure at the end of the day?
Fingers swell with heat and activity and shrink in the cold. Measuring in the evening captures the largest normal size, so the ring still goes on after a warm day. And remember the knuckle: the ring must clear it going on, which is why a slightly generous fit beats a snug one.
Do wide bands need a different size?
Often, yes. Wide bands fit tighter than thin ones because more metal contacts the finger. If you are between sizes for a wide band, consider the larger size. This converter translates the numbering; band width is a fit question for the jeweler.
My size is larger than US 14. What now?
The table stops at US 14, the end of the published chart, because sizes beyond it were not in the sourced data and this site does not extrapolate. Ask the jeweler for their extended chart; many carry sizes well beyond US 14.