The standard shoe width for men is D, and the standard shoe width for women is B. Unless the shoe is a non-standard width, it is not noted on the shoe box or label.
If the shoe is a non-standard width, it is noted underneath the tongue, along with other identifying information about the shoe. There are a few millimeters' difference between shoe widths of standard, narrow, wide and extra wide. Most of the additional width is located in the forefoot. In some cases, men can wear women's shoes for a more narrow fit, and women can wear men's shoes for a wider fit.