I am very curious as to what are the determining factors to repot regs?
It depends, on the size of the plant. I’ve read a foot of plant per gallon of soil. I like to have a full pot of roots when I transplant so I wait till I notice the plant gets some signs of being root bound. And if I’m going to keep flowering plants small I veg short in a 1/2 gallon then transplant to final pot just before switching to flower
When growth goes past the perimeter of the pot, pretty much, as a rule of thumb
I think everyone is going to have thier methods
Mine is by how much they are drinking
Generally I start in the equivalent of a solo cup and I use a 2 ounce shot glass for watering those… about 3/4 full.
I water 1/6th of the container’s volume (in sunshine mix #4) and at the beginning it takes 5 days to dry out, then 3 days to dry out and then when it’s down to 2 days to dry out I transplant to #1 pots (a little less than a gallon) and again start watering at 1/6th volume. Usually 2 cups per plant and again at transplant… every 5 days, then 3 and then at 2 days to dry out I transplant to thier next pot size whatever that is going to be. Generally by the end of week 6 in the #1 and sexing by preflowers, then the plants are going into thier forever home. At week 5 and a bit the plants will already be showing signs of wanting more root space but I always wait until they show preflowers before going bigger than a #1 pot.
Really does depend on some of the Genetics involved.I agree with @Kushking902 .Ive seen Pics Old BOG used to have on the original OG.He had Huge gigantic plants sometimes that were sometimes 6 ft tall in pots the size of paint cans.Huge plants itty bitty pots.I dont like to do that anymore they get rootbound amd you have to water like a psycho or have feed problems that turn into leaf problems then a down hill spiral