Take your left hand and wrap your thumb and middle finger around your other wrist....
if ...
it overlaps you are ======> Ectomorph
it barely touches =======> Mesomorph
Can't touch it at all ======> Endomorph
Most people fall in the middle of several categories ... Like I am an ecto-mesomorph because although i have a small frame with small bones I can pack on dense muscle and lift relatively heavy weights.
ecto's -- high metabolism, small frame and bone structure very lean
meso's -- moderate metabolism, average frame bone structure and can put on muscle the easiest
endo's -- slow metabolism, average to large bone structure and can put muscle on but have to worry more about fat intake and cardio to lean down ...