Ring Size Converter

How ring size conversion works

There is no formula for ring sizes — the four systems are four different charts laid over the same fingers. The honest anchor is the finger itself: inner circumference in millimetres. A US 7 ring has an inner circumference of about 54.4 mm and an inner diameter of 17.3 mm; every other system simply names that same ring differently — UK N, EU 54 and JP 14 on the standard chart this converter uses.

Reading the four systems: the US scale runs in whole and half steps from 3 to 13, with each half step adding roughly 1.3 mm of circumference. The UK scale runs through letters, with half letters between them. The EU scale is the friendliest — it is just the circumference in millimetres, rounded, so EU 54 means a 54 mm finger. The Japanese scale runs numerically from about 1 to 30 and steps fastest of all, roughly one JP size per millimetre of circumference.

Measure, don't guess: wrap a strip of paper or a flexible tape around the finger at the knuckle, mark where it overlaps, and measure the length in millimetres — that is your circumference. Measure at the end of the day, when fingers are at their largest, and measure the hand you will actually wear the ring on: dominant hands run about half a size larger. If you fall between two sizes, size up for wide bands (over about 6 mm), which fit tighter than narrow ones.

Brands vary — the caveat that matters: these are standard charts, and jewellers' lasts differ by up to half a size, exactly as with shoes. A US 7 from one maker can fit like a 6.5 or a 7.5 from another, and the same brand's comfort-fit bands run looser than its flat bands. For a surprise gift or an expensive ring, check that brand's own chart — or borrow a ring that already fits and measure its inner diameter.