How long does one's hair need to be in order to put in extensions?

Answer 1

does not have to be long at all . i have seen people with hair only 1.5 inches long and they were ableto get extensions

Answer 2

depends on the type of extensions and the "look" you're going for...
if you get the kind that are sewn in , then your hair needs to be long enough to braid
if you are getting "wefts" of hair that are put in with adhesive then your hair can be pretty short (like an inch long)
if you are getting one of the "strand by strand" methods done (which i personally think gives the best looking results) then hair should be a minimum of 4 inches