There really is no magic number of reps for either size and or fat loss. I suggest you go to the Weight training section on this site and read through it. They cover all topic with some starting recommendations. I've seen people people both bulk and lose fat (usually not at the same time though) with both rep ranges in the 5-8 range, and also in the 8-12 range. It also has a lot to do with how much you eat (or not eat), and your methodology (heavy weights, lots of rest between sets), or moderate weight with very short rest periods. Now, by text book standards, rep ranges from 1-6 are neuro geared, or strength enhancing. 8-12 are hypertrophy geared. Personally, when I was bulking, I did best skirting the two, and using reps in the 5-8 range, longer rest periods, with as heavy as I could go within that range, and eating A LOT. For Fat loss, I used more moderate weight, in the 6-12 rep range, with very short rest breaks, and eating much less. So, again, the is no magic number for reps. Please read through the weight training section at this site to get a better undertanding of the different methods involved.