中等身材 应该是medium height 除此之外 英语中亦有其他的表达方式
medium built 中等身材
average height中等身材
middle height
例句：
My father is of middle height.He is stout and strong.with a severe look on his face and with keen expressive eyes.
我的父亲中等身材,长得结实强壮,有一副挺严肃的神情和一双锐利而富于表情的眼睛.
He was a man of medium height with a slight paunch.His eyes shone with joy.At one look,you could instantly tell he was one of us,that is,a Mediterranean type.
他是个中等身材的人,大腹便便,眼睛里闪烁着喜悦,你一眼就可看出他是我们中的一员,即地中海人种.