We have rings from various brands and never do we have them all giving us the same information, so we've created our own in the hope to make it easier for selection.
The easiest way to tell your own ring size from here is that an EU ring size is approximately the circumference of your finger. So a ring size 54 is around 54mm the parameter of your finger.
UK: I+ / EU: 48
UK: J / EU: 49
UK: J+ / EU: 49.5
UK: K / EU: 50
UK: K+ / EU: 50.5
UK: L / EU: 51
UK: L+ / EU: 52
UK: M / EU: 52.5
UK: M+ / EU: 53
UK: N / EU: 54
UK: N+ / EU: 54.5
UK: O / EU: 55
UK: O+ / EU: 55.5
UK: P / EU: 56
UK: P+ / EU: 57
UK: Q / EU: 57.5
UK: Q+ / EU: 58
UK: R / EU: 59
UK: R+ / EU: 59.5
UK: S / EU: 60
UK: S+ / EU: 60.5
UK: T / EU: 61
UK: T+ / EU: 62
UK: U / EU: 62.5
UK: U+ / EU: 63
UK: V / EU: 64
UK: V+ / EU: 65.5
UK: W / EU: 65
UK: W+ / EU: 65.5
UK: X / EU: 66
UK: X+ / EU: 67
UK: Y / EU: 67.5
UK: Y+ / EU: 68
UK: Z / EU: 69
UK: Z+ / EU: 69.5
UK: Z1 / EU: 70
UK: Z1+ / EU: 70.5
UK: Z2 / EU: 71
UK: Z2+ / EU: 72
UK: Z3 / EU: 72.5
UK: Z3+ / EU: 73
We hope this helps a little.