Fitts’s Law (Wikipedia)
A dedicated encyclopedia article on Fitts’s Law, the design law also documented in Fitts's Law. Wikipedia articles are continuously edited, so year above reflects the access date (2026-06-24), not a fixed publication year.
License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/
Key points
- Paul Fitts published the original 1954 study in the Journal of Experimental Psychology, proposing a way to quantify how hard a target-selection task is.
- Movement time depends on distance to the target and the target’s width, following MT = a + b·log₂(2D/W) — the log₂(2D/W) term is the index of difficulty.
- Design implications well beyond “make buttons bigger”: the rule of the infinite edges (a target flush against a screen edge is effectively infinite in size along that edge — why macOS puts its menu bar at the very top), “magic corners” (where two infinite edges meet, exploited by Windows/Office for high-value controls), touchscreen target sizing, and handedness effects in radial/pie menus.
- Related laws: Hick’s Law (decision time vs. number of choices), the Accot–Zhai steering law (extending Fitts’s Law to constrained-path navigation like hierarchical menus), and throughput (bits/second, combining difficulty and time).
- Documented limitations: predictive accuracy degrades when distance and width both vary widely in the same comparison; the 1D formulation needs adjustment for real 2D pointing; applying it to eye-tracking/gaze interaction is contested, since saccadic eye movement isn’t the same kind of motor act as a deliberate hand movement.