Ring Size Chart and Converter

Ring sizes are all derived from the inner diameter or circumference of the band, so conversion is exact once you know the millimetres. US sizes step by about 0.8 mm of diameter (size 7 is 17.3 mm), UK sizes use letters from A to Z in half steps (N is 17.1 mm), EU and ISO sizes are simply the circumference in millimetres (54 is 54 mm around), and Japan numbers sizes 1 to 27 with size 13 at 17.1 mm diameter.

To measure, wrap a strip of paper around the base of the finger, mark the overlap and measure the length in mm for circumference, or measure the inner diameter of a ring that already fits. Fingers swell in heat and after exercise, so measure at room temperature in the afternoon. Bands wider than 6 mm feel tighter; choose a quarter to half size up. Knuckle size matters too: if the knuckle is much larger than the base, pick a size that just passes over it.