How to Pick the Right Hair Extensions. Here are the 5 things you should think about when buying hair extensions: 1. Length: Where do you want your hair to fall? I always recommend clients to go no more than 4 inches longer than their natural hair. The best way to see where you want it to lay is to start measuring it  from the middle of the back of your head. This is where your extensions will begin. -Sandee. Most hair extensions are available in these lengths:8”, 10”, 12”, 14”, 16”, 18” and 22”.  There are 24”...