In anime anatomy, on average, guys are a full head taller than girls. Girls will be about 6 heads tall and guys will be about 7. When drawing anything relating to anatomy, height is measured in heads. A head is exactly what it sounds like. It is the measurement of the top of the head to the chin. Just because someone has more heads, doesn't always mean they will be taller or larger though and it will differ from person to person. It all depends on the size of the head.