Sorry cant find it. But here a little calculation. Someone who is 180cm has 80kg of lean mass potential. Someone who isnt trained but lean would be around 65kg or so. So 15kg muscle to gain. If training correctly this person can gain 1-2 kg of muscle per month. So 6 month max 12kg muscle. Getting more muscle with training aint the hard part. Not getting fater while training for mass is the problem