Veronica, I'm a hair stylist and extension specialist, I've tried and worn every type of extensions there is. The minimum length for extensions is about 5-6 inches, if your hair is very thick you can sometimes get away with as short as 4 inches. I will caution you that unless you plan to wear them long term you need to be very careful about which method you choose. First of all there is no method that is completely without damage, the general rule is more extensions applied the more damage and slight thinning you will have. The best methods are ones that use wefts as opposed to strand by strand techniques. My favorite type of extensions are natural beaded row extensions there are several videos on YouTube showing this technique. If you truly want a no damage solution that is comfortable and looks natural then hair pieces are that way to go. Look up halo crown extensions, they are affordable 100% human hair and they do not damage your hair at all! Feel free to ask any questions you may have and I will try to help you figure out which method is the best for you