What's the average weight for a twelve year old girl?

What height? Average weight should be discussed in the context of height, since children experience growth in height at different times, expecially during 12 and up years of age. Although the average weight is 90 lbs, the average range (5th to 95th percentile) is from about 70 lbs to 140 lbs. Here is a calculator: http://goo.Gl/mku6o and here is a growth chart http://goo.Gl/ovrvo.
Ave in Us 90lb. The average weight of males of females of average height @12y is 90lb(41kg) according to the national center for health statistics charts. The range of normal weight varies with height & sex. Males from 60-135lb & females 65-140lb.