Fitts's Law

Fitts's law is a quantitative relationship in motor control research describing how long it takes a person to move a limb, such as a hand or finger, rapidly and accurately to a target area, showing that movement time reliably increases as the target becomes smaller, as the distance to be traveled increases, or both together. The psychologist Paul Fitts formulated the relationship in a 1954 study, expressing the difficulty of a given pointing movement as a single combined index derived from the ratio of movement distance to target size, drawing conceptually on ideas from information theory, and demonstrating that movement time increases in a highly predictable, logarithmic fashion as this index of difficulty rises. The relationship has proven to be one of the most robust and widely replicated findings in the study of human motor control, holding up consistently across a wide range of movement types, body parts, and even different sensory modalities used to guide the movement. Fitts's law has also found extensive practical application well outside its original laboratory setting, most notably in human-computer interaction and interface design, where it is used to predict and optimize how quickly a user can move a cursor or a finger to select an on-screen button, icon, or menu item of a given size located at a given distance, directly informing decisions about how large and how far apart clickable interface elements should be placed.