Personally, I don't count a “rep range” per say. If I'm going for size the target is a weight which i can do 8-12 reps, yes. But getting the TUT(Time Under Tension) on the muscles is whats key. For example if you throw that weight on a bicep curl and finish 12 reps in 20 seconds your not going to get the same results as doing a controlled, heavy life for a 45-60 second duration. This “time limit” will range from person to person and from muscle to muscle. It all depends on if the body group you are lifting are made of primarily Fast Twitch muscle Muscle Fibers, in which need less TUT to be exhausted properly, or Slow Twitch which obviously would be the opposite. Then of course there are groups which will be a mix of both. Usually muscle groups like biceps and triceps are MT fibers. Finding your Muscle Fiber type and the TUT in which should be applied is the best way to optimize muscle growth, or strength gains.