Depends on the wax to be honest. Like Magosienne posted the hair can't be super short, like just appeared hair, but it doesn't have to be fully grown out. A wax that requires no muslin strips and hardens on it's own before pulling it is best, in my experience, for shorter hair while with wax that requires a muslin strip it needs to be slightly longer. If you're doing waxing at home you can get small bottles of wax of both kinds from Sally's Beauty for under $5 each.