Fitts's Law
The time to acquire a target is a function of the distance to and size of the target. Larger, closer targets are faster to interact with than smaller, farther ones.
Overview
Fitts's Law is one of the few quantifiable, predictive models in UX. It states that the time required to move to a target is a function of the ratio between the distance to the target and its width. In practice: make interactive elements large enough and close enough to where users already are.
The implications are wide-ranging — why the macOS menu bar sits at the screen edge (effectively infinite height), why mobile tap targets should be at least 44×44pt, why primary actions should be larger than secondary ones, and why destructive actions benefit from being small and far away. The law isn't metaphorical; it's mathematical, and its predictions hold up consistently across decades of research.
Takeaways
- 01
Make interactive targets large enough to be acquired quickly and accurately — especially on touch devices where the pointing device (a finger) is inherently imprecise.
- 02
Place frequently used controls close to where the user's attention already is, reducing the distance that must be traversed.
- 03
Use screen edges and corners strategically — they act as infinite targets since a cursor or finger cannot overshoot them.
How to Apply This
Size primary actions appropriately.
The more important an action, the larger its target should be. A primary CTA should be significantly larger than a secondary link. Size difference communicates hierarchy and reduces acquisition time simultaneously — two benefits for one decision.
Put common controls near common starting points.
Don't make users travel far for frequently taken actions. Contextual actions should be near the content they affect. Confirmation buttons should be close to where users are already looking or pointing — not in a corner they have to hunt for.
Be deliberate with destructive actions.
Fitts's Law cuts both ways. A "Delete" or "Remove" button that is small, far from the user's current position, and visually de-emphasised is harder to hit accidentally — which is exactly the right behaviour for irreversible actions.
Common Misconception
Fitts's Law is often treated as a rule about mobile tap targets, but its implications extend to every pointer-based interface. The principle isn't "make things big" — it's that size and distance both determine how quickly and accurately a target can be acquired, and both should be considered together.
Origin
Fitts's Law was formulated by psychologist Paul Fitts in 1954, originally to model the speed-accuracy trade-off in human movement tasks. Based on information theory, it modelled motor control as an information-processing problem — the width of a target represents the tolerance of the movement, and distance represents the total movement required. The model was validated for mouse input in the 1970s and continues to hold for touchscreen interaction, making it one of the most durable predictive models in the field.
FAQ
- What is Fitts's Law?
- Fitts's Law is a predictive model of human movement that states the time to move to a target is a function of the distance to the target divided by the size of the target. In UX, it underpins decisions about button size, control placement, and touch target dimensions.
- How does Fitts's Law apply to UX design?
- It means that important actions should have large, easy-to-hit targets placed close to where users are already focused. Small targets far from the user's current position are slower and more error-prone to acquire — which is desirable for dangerous actions but not for primary flows.
- What is the minimum touch target size?
- Apple's Human Interface Guidelines recommend a minimum of 44×44 points. Google's Material Design recommends 48×48dp. These guidelines exist precisely because of Fitts's Law — below these sizes, the cost of acquiring the target (in time and errors) rises steeply, particularly for users with reduced motor precision.
- What is the 'infinite edge' in Fitts's Law?
- Screen edges and corners are effectively infinite in size because a pointer cannot move past them — the screen boundary acts as a wall. This makes the menu bar at the top of a screen, or controls pinned to edges, inherently faster to acquire than identically sized elements floating in the middle of the screen.
