There are three basic types of shoulders: narrow, average and broad. Many high-fashion models have broad shoulders. Determining which type of shoulders you have is just a matter of examining your overall proportions. Figuring out your shoulder structure can help you when it comes to choosing clothes, since certain styles of clothing look more flattering on specific types of shoulders.
Look in a mirror and notice how the t-shirt fits on your frame. A general rule of thumb is that a shirt's shoulder hemline should fall on the tips of your shoulders. If you have a t-shirt that follows this guideline, see how it fits you around your midsection. If it's relatively taught, then it's safe to say that your shoulders are not broad. If you're swimming in the rest of your shirt, you probably have a broad shoulder structure. On a similar note, if your shirt fits snugly around your waist but is extremely tight at your shoulders, you may have broad shoulders.
Look at yourself in a mirror, in the privacy of your bedroom or bathroom. Examine your unclothed torso with your arms resting at your sides. If your body forms a "V," or inverted triangle, shape from your shoulders to your waist, this is a good indicator that you have broad shoulders.
Examine the structure of your shoulders. Broad shoulders often appear flat, or perpendicular to the neck. Also look to see whether your shoulders have prominent bones protruding from them, adding to their overall definition. This may contribute to the look of broad shoulders.