Each ISO size is pinned to a diameter within 0.02 mm: 65 here means a 20.6 mm bore, checked on a calibrated steel ring stick 160 mm long.
UK to US conversion
Reading UK letters into US numbers reverses that alphabet: UK L is US 6, UK N is US 7, UK Q is US 8.5, one letter for every half a US size. Past UK Z the scale runs out of letters and switches to Z1 and Z2, which answer US 13.5 and 14. Since one letter can land on a US whole or half, a UK buyer converting to US should confirm the half, especially before ordering a size that cannot be adjusted after casting.
At this size, UK to US
One size up from UK V, US moves 0.5 to US 11.5 while UK steps to UK W. This size runs a 20.6 mm bore. For UK V, the US column here runs US 10.5, US 11, US 11.5, stepping a half size at a time.
Ring Sizes Around UK V US UK ISO / EU JP / KR Diameter (mm) Circumference (mm) 9.5 S 61 20 19.4 60.8 10 T 62 21 19.8 62.1 10.5 U 63 23 20.2 63.4 11 V 65 24 20.6 64.6 11.5 W 66 25 21 65.9 12 X 67 26 21.4 67.2 12.5 Y 68 27 21.8 68.5
Frequently Asked Questions Does UK V round up or down in US? Size for the warm hand and a clear knuckle; at larger sizes the gap between a ring that slides off and one that jams is only a fraction of a millimetre.
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Note ISO 8653:2016 sets the size as inner circumference in mm; France and Germany label by the same number, so a ring bought anywhere in Continental Europe needs no conversion. Japan and Korea share one scale: 1 gou is a 13.0 mm bore and each step adds a third of a millimetre, so US 7 (17.3 mm) is 14 gou and 14 ho. Russia and the CIS size by inner diameter in mm to the nearest 0.5, so US 7 is a 17.5 there. A band wider than 6 mm is usually sized up about half a size, and a finger can swing close to a full size between a cold morning and a hot afternoon, so measure warm and late in the day. See a number that looks off? Report an error on this page.