Sorry, I didn't realize most people probably couldn't read the text in the image I posted, after the auto shrinking the site does to it.

Basically, all adult humans are 7.5 heads tall. It varies somewhat, between 7.3 and 7.7, but the vast majority fall into the 7.5 heads range. 

Idealized figures use an 8-heads measurement, as this was a classic way of representing figures. If you consider the majority of early sculptures were done by artists whose goal was to represent kings and heroes who were "larger than life". It's also easier to divide evenly by 8. 

Most every part of the human body can be measured by the length of the head, or some variation of it.

Some examples:

the foot, from back of heel to tip of big toe, is the length of the head.

Forearm, length of head

Upper arm, length of head

Hand, from base of palm to tip of fingers is the length of the face, from bottom of chin to crown of the forehead. 

The head itself is 5 eye widths wide at its widest point. 

The mouth is measured by the corners falling directly in line with the center of each eye.

The list goes on and on, but it all comes back to the length of the head, in realistic proportion. 

Daz figures don't seem to keep within their own scale, as you can see by the measurement I just did on the image you posted. Tallest Vicky is 8.5 heads tall, next one is a solid 8. But each of the human females you provide are all 7.5 heads tall. 

 

~Shane