text: is this a good weight??? if u r 13 years old and 5ft 1in is 86lbs a good weight or is it 2 mush??? yes, i think it is.  the bmi (body mass index) charts put out by the government start at 58 inches and 91 pounds. according to their chart you could weigh up to 127 pounds!  if you weigh a little on the light side through your life, you will live longer for sure.  i am going to rethink the charts after seeing the answers coming in to your question.  stay light.