Height definitions; short, medium , tall etc ....

All depends on how you grow them, really. If you have good intense HID lighting, then you can have short tight nodes and control when to flower the plant based on how much room you have to grow them.

For example, I have 72inches of height to work with in my cabinet. After factoring in the distance of the pot, light, and hood, I could grow a 36" tall plant. So knowing that most indicas double their height in flowering, flowering a 16" indica would yield a 32" final height. And it did! Sativas are known for tripling their height when they flower, so I would have put a sativa plant into flower at 12".

Medium height = indica/sativa. Expect the plant to double in size when put into flower.
Medium/tall height = 80%sativa/20%indica. Expect the plant to double or triple in height.

Hmmmm, thanks purp'
I was hoping for some real numbers, eg
"Medium"= 24"-36"
"Tall"=36"-72"
or something.
Oh well, only one way to find out ! I've got a bit of headroom in my cupboard ....

Yeah I'd say medium = about 30inches, and tall possibly 60 inches (if its a real lanky sativa)

Ah, thanks.
That should help with decisions .... LST, scrog etc.

Cheers
Over & out

The first reply about said it all. The final height will largely be determined by how tall they are when you switch to a 12/12 light cycle. Indicas will roughly double in size. Sativas quite often stretch a bit more than that. The height quoted by the seller would be a maximum under natural light cycles. Sort of. You have to take the time quoted by sellers to harvest (especially for auto flowers) and total yield with a large pinch of salt. So, in summary, the finish height is pretty much up to you.