Jewelers often personalize rings according to a customer's specifications. When rings are engraved or customized in any way, the seller may not be able to accept returns, so you should measure your thumb to obtain your exact ring size before ordering jewelry. Measuring your thumb for a ring is a can be done by yourself at home or by a jeweler.
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Cut a 4-inch length of string or a 4-inch long, thin strip of paper. You can also find and print out a paper thumb gauge online.
Wrap the paper or string around the base of your thumb. Measure your thumb at the end of the day, when your thumb is the largest. Your body should be room temperature, because cold will cause your thumb to appear smaller, while heat will cause your thumb to expand.
Move the paper up and over your knuckle to check that it slides off easily. If there is too much resistance, loosen the paper slightly and check again. You want your ring to slide on comfortably, but it shouldn't be too loose.
Mark the paper or string where the two ends overlap.
Straighten the "thumb gauge" and use a ruler to measure the length that wrapped around your thumb. Measure in inches.
Convert the length of the paper to your ring size. Refer to this conversion chart:
Inches U.S. Ring Size 1 13/16 4 1 15/16 5 2 1/16 6 2 1/8 7 2 1/4 8 2 5/16 9 2 7/16 10 2 9/16 11 2 5/8 12 2 3/4 13 2 7/8 14