Fitts's law

Fitts's law predicts the time required to reach a target from the movement distance and target width. Its logarithmic form captures the speed–accuracy tradeoff in aimed movement.

Index of difficulty: A measure of task difficulty based on the distance to a target relative to its width. It is the logarithmic quantity used to represent how demanding a Fitts-style movement is.
Pointing device: A device that controls a pointer or selects locations through user input. Fitts's law predicts how quickly users can point with devices such as a mouse.
Paul Fitts: An American psychologist whose research established a quantitative relation between target difficulty and movement time. His 1954 experiments introduced the law now bearing his name.
Mouse pointing: The act of moving a computer pointer to select a location with a mouse. It is a standard interface task for applying Fitts's law.
Shannon formulation: A formulation of Fitts's law using log₂(1 + distance/width) as the index of difficulty. This widely used equation avoids a zero value when distance is zero.
Graphical user interface: A computing interface that represents information and actions through visual objects and controls. Its buttons and menus are targets whose size and placement affect selection time.
Human motor control: The study of how people plan, coordinate, and execute movement. Fitts framed aimed movement as a problem that could be measured and modeled.
Menu navigation: The process of moving through menus to locate and activate an option. Menu paths can constrain movement, making them useful for comparing pointing models.
Movement time: The elapsed time from the start of a movement to its completion. Fitts's law models how this duration changes with target geometry.
Touchscreen: A display that detects touch input at locations on its surface. Touch targets can be evaluated by their width and distance under Fitts's law.

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Computer mouseRelated: It helps explain why target size and cursor control affect pointing speed.