That's really not enough info to tell. ie, are you growing in dirt? The plants will grow slower in dirt. How's your lighting? Plants grow slower in poor light. How's your nutes. Plants grow slower without the proper chemicals. What are your temps? Plants grow slower in colder temps and rot in hot ones. What variety are you growing. Some grow taller than others.

As an example to compare, I am growing AK-47 in hydro and use cool tubes so I can get the lights right in the plants. My plants are about 2 feet tall at 30 days, some a little bigger. However I am not counting the time they spent getting roots in the cloner. If I am supposed to count that, then make it about 40 days, or 18 inches at 30 days.

Variables, man. Too many.