Proportions of the Head

To be able to do a 'perfect' portrait you need to learn some skills and tips. Starting with proportions within then head. The head can be divided horizontally into four equal quarters.

The first quarter measures from the top of the head to the hairline. The second quarter measures from the hairline down to the eyes in the middle of the head. 

The third quarter contains the most features. At the top of this section the eyes are usually level with the ears, and at the bottom of the nose is roughly level with the ear lobes. The final quarter stretches from the base of the nose to the chin with the mouth positioned just above the half way mark.

These proportions will only if we share the same eye level as the subject. they will become distorted if we view the head from above or below. 

Although the proportions of a head will vary form person to person and change slightly with age, there are some principles you can follow to improve your drawings. You can use these to check the general size, shape and position of the features in your drawings. If you view a head from the front, its width is approximately two thirds of its height. If you view a head from the side, its width is approximately seven eighths of its height. 

Some of the information was on one of my help sheet, hope it could help you too.