Fitts's Law

A predictive model of human movement that describes the time required to rapidly move to a target area as a function of the distance to the target and the target's size. Smaller and more distant targets take longer to reach and are more prone to errors. In accessibility, Fitts's Law explains why small touchscreen keys, buttons, and interactive elements are particularly challenging for people with motor impairments, tremors, or age-related motor decline. The law provides the scientific basis for accessibility guidelines recommending minimum touch target sizes (such as WCAG 2.5.8's minimum of 24x24 CSS pixels). Understanding Fitts's Law helps designers create interfaces that are usable by people with a wide range of motor abilities by appropriately sizing and spacing interactive elements.