2.54 cm
Computing the f-number of the human eye involves computing the physical aperture and focal length of the eye. The pupil can be as large as 6–7 mm wide open, which translates into the maximum physical aperture. The f-number of the human eye varies from about f/8.3 in a very brightly lit place to about f/2.1 in the dark. Basic Anatomy. Although small in size, the eye is a very complex organ. The eye is approximately 1 inch (2.54 cm) wide, 1 inch deep and 0.9 inches (2.3 cm) tall. The tough, outermost layer of the eye is called the sclera. It maintains the shape of the eye. The front sixth of this layer is clear and is called the cornea. How the Human Eye Works. The human eye can be compared to a camera which gathers, focuses, and transmits light through a lens to create an image of the environment. In a camera, the image is created on film; in the eye, the image is created on the retina, a thin layer of light sensitive cells at the back of the eye. The eye continues to grow, gradually, to a length of about 24-25 millimeters, or about 1 inch, in adulthood. A ping-pong ball is about 1 inch in diameter, which makes the average adult eyeball about 2/3 the size of a ping-pong ball. The transverse size of a human adult eye is approximately 24.2 mm and the sagittal size is 23.7 mm with no significant difference between sexes and age groups. Strong correlation was found between the transverse diameter and the width of the orbit (r = 0.88).
http://petapixel.com/2012/06/11/whats-the-f-number-of-the-human-eye/ http://health.howstuffworks.com/mental-health/human-nature/perception/eye1.htm http://www.afb.org/info/the-human-eye-its-functions-and-visual-impairment/5 http://www.tedmontgomery.com/the_eye/ https://en.wikipedia.org/wiki/Human_eye
what size is the human eye