How much taller will plants get after flowering?

Hey guys how's it going. I have a hydro setup and my plants have only been in veg for almost two weeks but not quite, they are about 15-18 inches or so right now and I think I have enough room for them to be no more than 3 feet tall full grown. How much taller will they get after flowering, will they double in size? If they do then do I need to flower them now even if they aren't showing pre-flowers yet? Thanks for your help.

Um yeah, I'd throw them into 12/12 now if you don't want them taller than 3'. 15-18" in less than 2 weeks? How far away is your light?

you could top and/or lst them. 2-3x's as big is about right.

funny, this thread is in another area with the EXACT title https://www.rollitup.org/newbie-central/511200-how-much-taller-will-plants-2.html