The best way to accurately find your ring size is to take a ring that fits you well and have it carefully measured by a jeweller, who should 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.
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.
If your knuckles are rather larger than the rest of your fingers it can mean that once your ring has passed over the knuckle area it ends up feeling loose and large when sitting in place on the finger - again, this is not uncommon. In this case, you might want to think about combining, or 'stacking', 2 or 3 (or more!) rings together, which will help to 'fill in' the loose space on your finger. If you are interested in a set of stacking rings please get in touch with me at firstname.lastname@example.org and I'll be happy to discuss some options.
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.