How do I calculate my ring size in cm in the UK?

To calculate your ring size in centimetres, first measure the circumference of your finger. Wrap a measuring tape or a piece of string around the base of the finger, mark where it overlaps, and then measure that length with a ruler. If you used a tape, read the number in centimetres directly.

Once you have the circumference in centimetres, convert it to millimetres by multiplying by 10. So if your finger measures 5.5 centimetres, that is 55 millimetres. UK ring size charts are usually given in millimetres, so you can then look up your size.

Be careful not to confuse circumference with diameter. Diameter is the straight line across the inside of the ring, while circumference is the distance around. Most home methods measure circumference, and that is what you compare to the chart. If you only have the diameter, multiply it by 3.14 to get the approximate circumference.

For accuracy, measure at least twice and at a time when your hands are warm. If you are between sizes, choose the larger one. If you are unsure, a jeweller can confirm your size for free, which is worth doing before you buy an expensive ring.