Fitts' 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. Formulated by psychologist Paul Fitts in 1954, the law states that larger, closer targets are faster to acquire than smaller, distant ones. In accessibility and interface design, Fitts' Law informs decisions about button sizes, spacing, and placement—larger touch targets benefit users with motor impairments. However, research has shown the law's speed-focused predictions may not fully capture accessibility needs, as error rates and the cost of mistakes matter more for some users than raw speed.