In today's fashion ring market, sizing can be a formitable task.
One of the best ways to determine your ring size is to go to a local jewelry store and actually try on a few rings. If you are interested in the new “comfort fit” variety – make sure you are trying on comfort fit rings. Not all rings these days have this new technological advancement built into the design so you might have to ask if the ring is a comfort fit.
One other way to determine if it is, is to look carefully at the inner and outer edges. In a comfort fit variety these edges are beveled and polished so that they slide over the knuckle easier – thus “comfort fit”.
When determining your size, it is best to size down ½ size from your non-comfort fit ring to a new comfort fit ring because of the beveled edges. So if you are used to wearing a 10 you might try a 9.5. But again, the sure way is to go a jeweler who carries these designs and try one on for yourself – no sense guessing and then having to make an exchange or worse yet losing the ring off your finger!