That's kind of an opened ended question:hubba: (not to be sarcastic, it can grow as much as yu let it) If yer concerned about stretch at this point then yu need to make sure yer lights are the
right strength, spectrum, and distance from the seedling. I always start out my babies under 6500k flourescent lighting. I use a few T5HO bulbs (about 10,000-12,000 lumens if I am starting a small bunch of youngins) so that I am not blasting them
with a load of intense lumens. I have them about 12-18" away from the crib so that I can remove the humidome from when I need to. Having that much (and no more) will give them a plenty of light to grow without stretching. Once they reach about 6" tall (and have 4-6 nodes) I move them into a higher amount of light (about 40-60,000 lumens) for a week or so before putting them into the super veg for a few weeks, under which they get about 100,000 lumens (in a 3.5'x3.5' area) until switching over to flower.
That's probably more information than yu were asking for:doh: hope it helps:farm: