The best way to accurately find your ring size is to visit a jeweller for a fitting. You could also take a ring that fits you well and have it carefully measured by a jeweller, who will be able to give you a UK ring size (eg. 'L', or 'N 1/2'). Bear in mind that a broad ring style, for example a wide wedding band type ring, will fit differently to a very narrow ring, so be sure to choose a ring that is comparable in size to the one you're planning to purchase.
Avoid using string or paper to measure your finger, as it is not accurate enough. If you are unable to get to a local jeweller or have any difficulties finding your size get in touch with me at firstname.lastname@example.org and I'll be happy to help.
It is common for hands and/or fingers to swell slightly in the heat, and contract in the cold - some people find this fluctuation to be quite significant, so it's worthwhile taking time to think about how your hands are feeling at the time of measuring. Measure several times, and at different times of the day, in order to estimate an average size.
Your ring should be large enough to fit over the finger joint, and sit snugly on the finger.
It is the customer's responsibility to ensure that you have requested the appropriate size for your needs and I will always craft your ring to your specified size. If, however, on receipt of your ring something doesn't seem quite right, please feel free to get in touch and I'll be happy to advise.