Proportion is how the sizes of parts compare. A drawing can be any size on the page and still look right, as long as its parts compare the way they do in real life. That is the same idea as a ratio, which you may know from the Math Ladder's Ratios topic.
Artists measure with a unit: one part of the object used as a ruler for the rest. "The bottle is four caps tall." "The window is two panes wide." Then they draw the unit and lay it off on the paper the same number of times.
Key idea
Choose one part as a unit, count how many units long the other parts are, and keep those counts the same in your drawing.
Why it works
Your memory exaggerates the parts you care about and shrinks the rest. A measurement does not. Counting in units keeps the relationships true even when your drawing is bigger or smaller than the object, because a ratio does not depend on size.
Worked example: Draw the bottle
A bottle is 4 caps tall. In your drawing, the cap is 2 cm tall. How tall should the whole bottle be?
- The bottle is 4 caps tall.
- Each cap is 2 cm in the drawing.
- $4 \times 2 = 8$.
Answer: 8 cm.
Worked example: Going backward
A lamp is 3 shade-heights tall. You drew the whole lamp 15 cm tall. How tall should the shade be?
- The lamp is 3 shades tall.
- So one shade is the whole height divided by 3.
- $15 \div 3 = 5$.
Answer: 5 cm.
Common mistake
People draw parts at the size they feel they are, such as a big face and small hands, instead of the size they measure. Before you draw a part, ask "how many units is it?" and count.
You will use head heights for faces and figures later in this course: Figure Proportions in Heads.