It can be hard finding shoes that are the right size. If you've ever bought shoes because they looked nice without taking the time to test them out in the store, they may be too big or too wide. The biggest test for if your shoes are too big or wide is if they are comfortable after a day of wear, but there are some other surefire signals that you'll need to replace a pair of shoes that don't fit you properly. The sooner you determine if your shoes fit right, the sooner you can ensure that you will have healthy feet and be free from pain after a day on the go.
Put on the shoes. This includes lacing the shoes fully (if they have laces) and tightening and tying the laces or otherwise fastening the shoes. If the shoes only fit your feet when you cinch the laces so that the toe of the shoe is much wider than the middle, or if the shoe lace panels overlap at all, the shoes are too wide.
Walk around the room in the shoes. Take note if your feet are sliding backward and forward or from side to side as you walk. If they slide around or you have to curl your toes to keep the shoes from slipping, the shoes are too big or too wide. If you are wearing pumps and your heels slid out of the shoes, they are too big. If you can see clear gaps between your foot and the side of a pump, they are too wide.
While seated, feel for your big toe inside your shoe by squeezing the toe of your shoe. You should be able to feel a small, but not a large, gap in front of your toe. If you can compress the top of your shoe to the footbed of the shoe in front of your toe, the shoe is too big.
Wear the shoes for a day, and take note at the end of that day if the shoes were comfortable or your feet slid around in them.