Learning how to wear a belt fashionably can be as easy as keeping three key components in mind: color, size and the overall proportion of an outfit. That means sizing up the amount of fabric. For example, if you are wearing a long dress, opt for a wide belt. This way the proportions are kept in check. Similarly, short dresses, particularly ones that fall above the knee, often look best when paired with a skinny belt. However, for a sexy look, go ahead and choose a wide belt.
Here the belt is wide because there is a lot of fabric (the dress).