You can estimate proportions and then check them with a fair degree of accuracy by employing what is called the thumb-and-pencil method of finding proportions. This is done by simply placing your pencil or pen in your hand and then holding it at arms length between your eye and the object that you plan to draw. Here is how:
(1) Hold your body rigid and extend your dominant arm (usually the right arm), pencil in your hand, to its full length.
(2) Place your thumb against the pencil as a gauge (sliding it up and down or to the left or the right, depending on the unit of measurement you wish to establish).
(3)Bring the pencil on a line with your eye and the object that you are measuring.
(4) Try to find one part by which you can then measure the rest of the object. In the diagram above, the head is used as a unit of measurement to determine the length of the subject's body. This is done by aligning the tip of the pencil with the edge of the snout, and the thumb is resting on the pencil to where the head ends at the start of the neck. The tiger above is thus, six heads in length.
(5) Once you find a part to which to measure the rest of the parts of the object, you can then proceed to put in the object’s details, still using the same scale of measurement in which you established.
An example of how to use your pencil as a measuring stick to find the height and width of the house with the use of your pencil and thumb. You can also find the angle of the roof with this method. In drawing the house (as shown above), the height of the chimney might be taken as a standard of measurement. Hold the pencil upright, the top on a line with the chimney top. Now move the thumb downwards until the end of your thumb comes between your eye and the bottom of the chimney. Then draw the chimney. Repeat this measuring operation, finding where the length of the chimney corresponds to other parts of the house. Your pencil can be moved between the house and your eye and by using the chimney length as your standard of measurement, the corresponding length and width of the house can be estimated.With the pencil and thumb measuring technique, you can even find the angle of an object, such as the house’s roof. Just hold your pencil parallel with the object (in this case the roof). Then, without changing the position or angle of your pencil, just bring it down to your paper and make a light stroke indicating the angle.
Likewise, by sliding the pencil up or down so as to increase or decrease its length between the points ‘a’ and ‘b’, (shown above) you will be able to check the height of an object as shown below. The same principle applies for heights and lengths/widths.
Above is a demonstration of the height of a cone being checked, while the bottom demonstrates the width of the cone being checked.
This thumb-and-pencil method of checking is easy to understand once you experiment with it. Be sure, however, that you do not change your position or distance from the model once you have started to check, since distance and position change the appearance and size of any object under study.
