Jeans are a staple in everyone's wardrobe. The wide array of sizes and styles available can make it hard to understand if the jeans you are trying on fit or not.
When trying on a pair of jeans, the first thing to notice is the waist. Waist sizes differ at every clothing store, so do not be surprised (or feel down) if you usually wear an 8, but need to find a 10. Make sure that the jeans fit snugly at the waist, but are not too tight. You should be able to fasten the button without hesitation. Also, it is important to understand that the different types of jeans should "hit" in different areas. For example, low-rise jeans should fit below your waist, snugly but comfortably.
The next thing to notice is how the jeans fit through the thighs and butt. Fitted jeans are known to be snug to these areas. Be sure that the jeans are fitted and not baggy. Make sure, however, that the jeans are not too tight; if you are expanding the jeans, or the seams look to be stretching, the jeans do not fit. If there is an excess amount of material in the back of the jeans, they also fail to fit correctly. Determine which kind of fit works for your thighs and butt. Bootleg jeans fit differently than straight leg jeans; trying these on will help you to know which fit your body type.
The final thing to pay attention to when looking at jeans is to note how the bottom of the jeans fit. At the ankle, the jeans should not be tight (unless you have chose a tapered leg jean). The pair of jeans should be relatively loose at the ankle, allowing you to wear them with shoes. If the end of the jeans gathers too much at the bottom, the jeans are too long for you and need to be shorter.
When trying on jeans, grab multiple sizes and types. Size and types fit differently from store to store. Know the difference between fitted and tight to make sure you are getting the right size.