Physics of Interaction · principle
Fitts's Law
Playable Play this law (~3 min)or keep reading below ↓
The time to acquire a target is a function of the distance to and the size of the target. Bigger, closer targets are faster and easier to hit — which is why primary actions should be large and within easy reach, and why tiny close-together tap targets cause mistaps.
See it on a real screen
Same screen, same task. The big pay button sitting in the natural thumb arc is fast and forgiving; the tiny corner link is a game of darts. It's why Apple asks for 44 pt targets and Duolingo's CHECK button is enormous.
Where it comes from
In 1954, psychologist Paul Fitts had subjects tap back and forth between two metal plates with a stylus, varying the plates' width and the distance between them. Movement time followed a precise law derived from Shannon's information theory: harder targets (smaller, farther) take predictably longer. Half a century later, the same law decides how big your phone's buttons are.
Origin: Fitts's 1954 reciprocal stylus-tapping apparatus — two metal plates on a desk
In the wild
- Apple iOS
Apple's Human Interface Guidelines require a minimum 44×44pt touch target — Fitts's Law turned into platform policy.
- Google Material Design
Material specifies 48×48dp minimum touch targets with ~8dp spacing between them.
- Microsoft Windows
Screen corners and edges are 'infinitely' hittable — you can throw the cursor at them without overshooting, which is why Start lives in a corner.
- Duolingo
The big full-width green CHECK button is impossible to miss — the single most-pressed control gets the largest, closest target.
Further reading
Don't just read it — feel it.
Play the 3-minute game and let your own reactions prove the law.
Play the lesson