What is Fitts's law in UX design?
Fitts's law is a predictive model of human movement that describes the relationship between the size of a target, its distance from the user's starting position, and the time required to reach and interact with it. Formulated by psychologist Paul Fitts in 1954, it states that larger targets and shorter distances produce faster, more accurate interactions.
In interface design this translates directly to decisions about button size, touch target size, element placement, and the distance between related interactive elements.
Why does Fitts's law matter for interface design?
Small buttons placed far from where users' attention naturally falls cause errors, slow interactions, and frustration, especially on mobile where finger precision is limited. Fitts's law provides a principled basis for decisions that designers sometimes make intuitively: why primary actions should be large and centrally placed, why destructive actions like delete should be small and physically separated from safe actions, and why floating action buttons work well for the most frequent task.
How to apply Fitts's law in UX design
Size primary interactive elements generously. On mobile, touch targets should meet the minimum 44x44 points recommended by Apple and Google. Place the most frequently used actions where users' attention and thumbs naturally rest. Keep related actions close together and separate dangerous or irreversible actions from common ones by distance as well as visual treatment. Corner and edge positions on a screen have effective infinite width on one side, making them fast targets, which is why screen corners and edges are valuable real estate for persistent controls.
What is the relationship between Fitts's law and accessibility?
Fitts's law directly supports accessibility. Users with motor impairments benefit significantly from larger touch targets and shorter distances between interactive elements. Meeting minimum touch target sizes is both a usability best practice and a requirement under WCAG 2.5.5. Designing for Fitts's law and designing for accessibility are largely the same activity.