In general, a woman's 28-inch waist is small to medium, while a man's size 28 is extra small. Sizing may vary depending on age, manufacturer and country.
If a young girl has a 28-inch waist, her sizing may fall into the XXL size for her age range. Junior girls with this measurement may wear a size 6 or 8, small to medium, as a 28-inch waist on average falls in the middle of that range. These measurements are for generic pants. However, jeans have a different fit, and women may find they have to increase a size or two. For example, women who have a 28-inch waist might wear 6 or 8 in jeans, but they may wear a size ranging from 6 to 10 in pants or skirts.
Since men tend to be of a bigger stature than women, their sizes run much smaller. Men who have a waist that measures 28 to 29 inches usually have to look for pants in extra small, or XS. However, sizing for loungewear, such as pajamas and robes, is a bit more generous. Since a 28-inch waist is right on the cusp, a man may wear either an extra small or small in this type of clothing.