Depends on the strain, your lighting, your available headroom, and to a certain extent...your experience level. The most successful gardeners set-up and operate under the 1 foot per gallon rule of thumb as a guideline, not a hard and fast rule.

There are so many different strains and crosses that a hard and fast rule is unobtainable. For instance...a sativa dominate cross will likely have a taller/more lanky growth habit than an indica dominate cross.

If growing from bagseed, it's a good guideline. If you've purchased the seeds, you can read-up on the habits of that strain online.