The Vitruvian Man (1492) is the famous sketch by Leonardo da Vinci showing the various geometrical proportions in the human body. Da Vinci drew this sketch based on a description by the Roman architect Vitruvius (1st century B.C.) In De Architectura, Vitruvius describes many aspects of architecture, including mensuration. It is his suggestion that the proportions in the human body can be related to geometrical figures, i.e. the human body has a universal, mathematical perfection.

Da Vinci's sketch shows a human figure with two sets of arms and two sets of legs. The horizontally and vertically stretched arms and legs touch a square indicating the relationship between the arm span and height of the man. At the center of the square are the man's genitals. The diagonally stretched arms and legs touch a circle, with the navel at its center. An interesting observation is the consonance of the square and the circle (cf. Squaring the Circle). In classical history, the square represents the physical world (e.g.the four elements, the four wind directions), while the circle represents the spiritual world (mother earth, with the navel at its center.)

There are many different geometrical proportions in da Vinci's sketch. However, the most important one is the Golden Ratio, and especially the division around the navel: the ratio of the length from the man's head to the navel and the length from the navel to his feet is equal to the ratio of the length from the navel to his feet and the total height of the figure. But the golden ratio is present in all scales. For instance: the length of the upper arm divided by the length of the lower arm and stretched hand is equal to the length of the lower arm and stretched hand divided by the length of the entire arm.

Text accompanying Leonardo da Vinci's sketch of Vitruvian Man:

Vitruvius, the architect, says in his work on architecture that the measurements of the human body are distributed by Nature as follows that is that 4 fingers make 1 palm, and 4 palms make 1 foot, 6 palms make 1 cubit; 4 cubits make a man's height. And 4 cubits make one pace and 24 palms make a man; and these measures he used in his buildings. If you open your legs so much as to decrease your height 1/14 and spread and raise your arms till your middle fingers touch the level of the top of your head you must know that the center of the outspread limbs will be in the navel and the space between the legs will be an equilateral triangle.

The length of a man's outspread arms is equal to his height.

From the roots of the hair to the bottom of the chin is the tenth of a man's height; from the bottom of the chin to the top of his head is one eighth of his height; from the top of the breast to the top of his head will be one sixth of a man. From the top of the breast to the roots of the hair will be the seventh part of the whole man. From the nipples to the top of the head will be the fourth part of a man. The greatest width of the shoulders contains in itself the fourth part of the man. From the elbow to the tip of the hand will be the fifth part of a man; and from the elbow to the angle of the armpit will be the eighth part of the man. The whole hand will be the tenth part of the man; the beginning of the genitals marks the middle of the man. The foot is the seventh part of the man. From the sole of the foot to below the knee will be the fourth part of the man. From below the knee to the beginning of the genitals will be the fourth part of the man. The distance from the bottom of the chin to the nose and from the roots of the hair to the eyebrows is, in each case the same, and like the ear, a third of the face.