According to Watch Cases, the average wrist size for adults is 7.17 inches. This measurement varies according to the height, build and age of a person.
To accurately calculate a person's wrist size is to measure it. Placing a soft measuring tape around the wrist bone and recording the information at the point where the measuring tape meets, results in the person's wrist size. If a soft measuring tape is unavailable, a string or ribbon may be used in it's place. The material can then be measured along a straight ruler to arrive at the person's wrist size. Whatever material is used, it is important to keep it snug, but not tight, for accurate results.