Fitts’s law

Fitts’s law is a predictive model of human movement, stating that the time required to move to a target is a function of the distance to the target and the target’s size: a larger target, or one closer at hand, can be reached faster and more accurately than a smaller or more distant one. It was formulated by the psychologist Paul Fitts in 1954, based on research into human motor control, well before it had any connection to computing.

In user interface design, Fitts’s law is used to reason about the placement and sizing of interactive elements. A button that is large or sits at a screen edge or corner, where the cursor’s movement is effectively stopped by the edge of the screen rather than needing to be precisely aimed, is faster and easier to hit than a small button floating in open space. This is why operating system menus conventionally place system-wide commands in a screen-edge menu bar, and why frequently used controls tend to be made larger than rarely used ones.

The law is one of the more directly quantitative results imported into software design from experimental psychology, and it sits alongside Tesler’s law as part of the broader tradition of treating interface design as subject to measurable laws of human perception and motor behavior rather than as pure aesthetic judgment.

See also

• Laws and principles

References

• Fitts, Paul M. (1954). The Information Capacity of the Human Motor System in Controlling the Amplitude of Movement. Journal of Experimental Psychology, 47(6), 381–391.