When drawing, you can figure out the proportional relationship between one object and another by using your pencil as a measuring device. The method will not provide exact measurements, but it is an easy, practical tool that you can use to approximate proportion.
Choose how far away from your subject you will stand. Once you’ve chosen a distance, you’ll have to stick with it. Any measurements you take will change if you decide to move closer or farther from the subject.
Hold your pencil at arm's length either vertically or horizontally, depending on if you want to measure height (top to bottom) or width (left to right), respectively. Bending your arm will make it harder to take consistent multiple measurements.
Align the top of the pencil with the top of your main subject to measure height. If you want to measure width, align the top of the pencil with the left or right side of your main subject, depending on which hand you’re holding the pencil with.
Hold your thumb on the back of the pencil - towards you - and align the end of your thumbnail with the bottom of your main subject to measure height. For width, align the end of your thumbnail with the other side of your main subject, opposite the pencil’s top. The portion of the pencil from the top to your thumbnail gives you an approximate height, or width, for your main subject.
Compare the other objects to the height or width of your main subject by lining up the measured portion of your pencil to the surrounding objects, as you would a ruler. This will allow you to see how much shorter, taller, narrower, or wider they are compared to your main subject. For example, you will be able to tell if another object is three times higher than your main subject, or if it’s half as long.
Use your approximated proportions in your drawing. For instance, if you are drawing a statue in front of a building, and you used your pencil to figure out that the building is four times the height of the statue, you can use this to draw these objects to scale.
You can use the height of your main subject to measure the width of an object as well, and vice versa. For example, if you measured the height of a statue, you can turn your pencil vertically to find that the statue is only 1/3 wide as it is high. You can use the height of the statue to find that the building in the background is three times as wide as the statue is high.
You can use your pencil to measure the height or width of an object when drawing from a photograph. Place your pencil on the photograph and align the top of your pencil with the top or side of an object, and your thumbnail to the bottom or opposite side of the object, depending on if you are measuring height or width. You can then use the measured portion of your pencil to compare the proportion of the measured object to another.