A comfortable ring should slide over the knuckle with light resistance and sit securely without pinching. Because fingers change slightly with temperature and activity, one quick measurement is rarely enough.
Measure a ring that already fits
Choose a ring worn on the same finger and hand as the new piece. Place it on a ruler and measure the inside diameter across the widest point, without including the metal edge. Compare that measurement with the size chart supplied for the product.
Measure more than once
Measure near the end of the day, when your hands are at a normal temperature. Avoid measuring immediately after exercise, in very hot weather or when your hands are unusually cold. Repeat the measurement on two or three days to confirm the result.
Allow for band width
A wider band can feel tighter than a delicate band in the same size. If the design has a broad shank or several stacked bands will be worn together, ask whether a slightly larger size is recommended.
Keep the knuckle in mind
If your knuckle is noticeably wider than the base of your finger, the ring must pass over it without becoming loose once in place. A professional fitting can help balance both measurements.
Home measurement is a useful starting point, but an in-person sizing is the safest choice for an engagement ring, a wide band or a design that may be difficult to resize.