The following guide shows the ring sizes in millimetres (mm) and the equivalent
USA/Canada sizes, and UK/Ireland/Australia and New Zealand sizes.
MM USA UK / Ireland
50mm - 5.5 K
52mm - 6 L
53mm - 6.5 M
54.5mm - 7 N
55.5mm - 7.5 O
57 mm - 8 P
58.5 mm - 8.5 Q
59.5mm - 9 R
60.8mm - 9.5 S
62 mm - 10 T
There are a couple of ways to find out your ring size, the best method really is to go a local jeweller that you trust and ask them to measure your finger using a jewellers ring sizer, and find the exact size that fits you both snugly and comfortably. However if this is not an option and you are in a massive rush, there are some home methods. You need to be very careful doing these home methods though, as a half millimeter out and you could find yourself with a ring that's either falling off or too tight.
HOME METHOD 1
One way to find your ring size is to measure a ring that fits on your chosen finger. To do this measure the diameter of the inside of the ring (which is at the widest point) and use the guide above to find your ring size in USA/Canada sizes, and UK/Ireland/Australia and New Zealand sizes.
HOME METHOD 2
1. Wrap a piece of string or a strip of paper around your finger. 2. Mark the point where the two ends meet.
3. Measure the string or paper against a ruler to get the circumference of your finger in millimetres.
4. Use the guide above to convert the millimetre dimension into the system used in your country.
Good Luck :)