In northern Virginia, KOs are generally pruned down to about two feet tall each spring in March. By fall, they are easily 6x6. I have never seen one that hasn't been pruned.

There are 5 kinds of KO roses. What kind are you asking?

I have red double KOs as do many of my neighbors. (they were here when we bought the house) Some people that use lawn services have them pruned to about 18" in February and theirs by August are 4 ft tall. A few I've noticed didn't prune that short, maybe to 2.5' and theirs are over 5 ft tall. It will just depend on conditions and how much they are pruned to start the growing season I imagine.

The original KO in my z4 area rarely gets more that 2' tall & has significant cane die back. I & most of my rose growing friends in this area find that it also has poor winter hardiness & is slow to wake up in the spring. Yet when visiting family in Atlanta, GA, I see KO's growing like cecily describes them above.

In central NJ, Knock Out gets to 6' x 4'. The Blushing Knock Out (a mutation or sport of the original, as is Pink Knock Out) got to 7' x 4' before I hacked it back a few weeks ago.

I would say to plan for at least 4 x 4 ft. bushes by end of season. How much you have to prune down in the spring will depend a lot on how they do over the winter. If like the last two winters you'll probably have to prune very short to start with because of die back, like 6 or 8 inches. In that case they may only reach 2 or 3 feet in height. However, if the winter is milder they may start out at two foot high and go from there.

summer, I am talking about the double red. I didnt know they could get up to 7ft!

I am in zone 6a, my double KOs stay short and small, they're about 2'x2' for the bigger ones. The single red KOs can get to 4x5 here.

There are three planted as a triangle in the corner island of a now-closed Ryan's parking lot, and those three plants (never pruned) are a solid mass about 6' high and 12' across. Alas, they now have RRV, so they aren't long for this world. These are by far the biggest ones I've seen.

John

Regular Ko's around here get to be 5ft-6ft high by 4ft-5ft wide...

Our Double Knockouts are 3.5ft-4ft tall x 3ft-4ft wide...

It's no longer mine. I gave mine away when it overtook four other roses. My friend sat the pot on the side of the house. Her daughter started complaining about the monster outside her window. after a few years I went to visit and the KO was the monster. It was at least 8 ft tall and bigger around. I've never seen a rose that big. the pot was still sitting on the ground and was busted, the base of the rose was as big around as my leg!