Well it doesnt really go by how many plants but more on the side of how much canopy you have. This depends on the size of your plants which is dictated on your style of growing. If your doing SOG you will be able to grow more than if you were just growing plants for awhile and then flowering them. SOG method will give you more plants but they will be kept smaller. You could also get more plants in if you have a light rail and you can use LST and super cropping as well to control how and where your plants grow.