Veg to Flower differential

What up world! I have a small indoor setup that I built myself. The dimension is 4' x 3', with a little over six feet of headroom. I was just wondering....about how much of a growth spurt will these babies go through when the I switch stages? I cannot tell you what strain, just some odds and ends out of some decent midgrade. This is the beginning of the fifth week from germination of the eight, and they range from 5 to 8 inches tall. I have about 3.5 to 4 feet of open headroom the way my setup is now. Any input is very much appreciated. I have become obsessed with learning this.

Thanks ---

Bread.ed

(That's "Breaded"...not "Bread Ed")

When you start flowering they can/will double or even tripple in height. What type of lighting are you using for vegg & flowering?

They are vegging under a six bulb T5. I have a couple of options for flowering, but haven't chosen yet. Thanks for the iput Toke!