A well-fitting ring slides over the knuckle with gentle resistance, then rests comfortably at the base of the finger. It should not pinch, leave a deep indentation, or spin constantly during ordinary movement. Because fingers can change size through the day, judge fit when your hands are at a typical temperature rather than immediately after being outdoors in cold weather or exercising.
For the best measurement, use a professional jeweler's sizing tool or follow the sizing guidance provided by the maker. Measure the specific finger where you plan to wear the ring; fingers on the same hand are not always the same size. A wide band generally feels snugger than a narrow one, so ask whether the design affects the recommended size before ordering.
If you are between sizes, consider the ring's width, shape, and how often you will wear it. A ring intended for daily use needs to remain comfortable through ordinary activities, while a decorative ring may be worn less often. Avoid guessing from a measurement taken with string, which can stretch or compress. When in doubt, have a jeweler assess the fit in person.