The average length of the adult hand varies by gender. For adult men, it's 7.44 inches (18.9 cm), while among adult women, it's 6.77 inches (17.2 cm). The difference in the lengths of the hands between genders is the result of a concept known as sexual dimorphism. Similar gender-based proportional differences are found throughout measurements of the different parts of the human body.
Sexual dimorphism describes the differences that occur between the separate sexes of the same species. The difference in the length of the adult hand in humans is one example, while the difference in the coloration of male and female birds is another. Exact distinctions between genders vary greatly in nature.
Although the average length of the hand differs from person to person and by gender, it actually still has some proportionality relative to the individual. One example is that a hand with fingers extended will cover the face exactly. These types of ratios are independent of a person's gender.
The average adult hand breadth for a male is 3.3 inches (8.4 cm). For an adult woman, the same measurement averages 2.9 inches (7.4 centimeters). Just like the length of the hand, the breadth has some proportional relationships to the body that are independent of gender. The breadth of the hand, for example, is the same distance from the bottom of the chin to the tip of the nose.
The human hand itself has several interesting proportions within its own structure. The fingers of the hand, which are broken down into four bones from the wrist to the finger tip, express a very close approximation to a mathematical formula known as the Fibonacci sequence. This can be seen because each of the bones from the tip of the finger to the wrist is roughly 1.6 times larger than the bone that precedes it. The ratio of the length of the hand to the length of the forearm also is 1.6, continuing the sequence. This type of pattern is found throughout nature.
The various dimensions of the hand have played different roles in measurement throughout history. One measurement is actually called a "hand" and is used to record the height of horses. The original measurement was the breadth of the hand, but it has since been standardized. The official measurement of a hand in relation to horses is 4 inches (10 centimeters).