How big before i start flowering

so how many weeks before i should start going 12/12, im about 4 weeks and they are about 16''now

Flip the switch.

are they from clones?

you should wait at least 12". so you would be fine if you started now. they are going to at least double, most likly triple there size till they are all done ready to smoke.

they from clones?

no clones, how many weeks till harvest u think

depends on the strain. so they are from seed? 16" in 4 weeks?

id say my biggest is about 16"

i have small space though