Once the plants go into flowering they can double or triple in height. If you want to keep the plant about 4 feet you should probably not veg them anymore than 1 1\2 feet. It varies with different strains, some strains will jump to 6 ft pretty easy. Since most of the plants are grown under ideal conditions with a lot of TLC, they can really get big and bushy and fill up a room pretty easy.
Anymore I am just a closet grower.......so I donā??t do the Big monster crops like others.
You just have to guess how much the plant might grow. Some strains are short and stocky some are big and bushy. If you bought the seeds usually the description will give you an idea about the growth characteristics.
Good luck