Fitts's Law
The time to acquire a target is a function of the distance to and size of the target.
Key Takeaways
Touch targets should be large enough for users to accurately select them.
Touch targets should have ample spacing between them to prevent accidental taps.
Touch targets should be placed in areas of an interface that allow them to be easily acquired, minimizing the distance users must travel.
Origin
In 1954, psychologist Paul Fitts studied the human motor system and discovered that the time required to move to a target depends on the distance to it, yet relates inversely to its size. He identified a speed-accuracy trade-off: rapid movements toward smaller targets produce higher error rates. This principle became foundational to user experience and interface design, particularly influencing the convention of creating larger interactive buttons for mobile devices and minimizing distances between user attention areas and task-related controls.