Hello,
A 1/4 scale male head would be around 2.25 inches, from chin to top of head (Minus hair). Full figure would be 18 inches (For an 8 heads tall figure)
1/3 scale would be 3 inches.
Just keep this in mind- The "Ideal" size of an adult male head is 9 inches. Ideal female- 8.25 inches. So just scale accordingly (By dividing the scale into the actual size)
Hope that helps.
Best,
Rick Force~
BTW- 1/6 head is- 1.5 inches
1/8 is- 1 & 1/8 inches..... Also-a good idea is to make a photocopy of a few different head views in a few different scales for quick reference. An artist whose work I've always appreciated for great figure drawing and proportions is Andrew Loomis. Jack Hamm is another. There are many, but look those guys up. You'll be glad you did.