When deciding on and choosing how long you want your extension hair, you’ll want to keep in mind the length of your own hair because it’s a good idea to try to add 2 to 4 inches to your own hair for blending purposes.
You can add more if you like, but keep in mind the finished look. Your shorter hairs will be on top of the longer extension hair for covering attachment areas.
To accomplish a general idea of how long 16 inch, 18 inch, 20 inch hair extensions will look, use a tape measure: You can hold the tape measure to begin just above your ear. When you are looking in a mirror, pull it down 14, 18 and 22 inches (begin mid ear) in front of your shoulder. If you’d like to see the back, have someone help you and pull the tape measure down to the desired length.
Typically a taller person will look better in much longer hair but the same length might shorten a more petite figure. Decide on the range you’d like the extension hair to fall and where your finished result should be and you’ll have a good idea of what length extension hair you want to get.