Fitts Law
Selecting a small or distant target generally takes more time and precision. Control placement contributes to interaction effort as well as appearance.
The law concerns movement towards a target. It does not independently explain whether someone understands a label, wants to buy or trusts a store.
What it means
Consider distance and size together. The area that actually accepts interaction matters more than a decorative background that merely makes a button look larger.
Origin of the concept
The law comes from experimental research on movement and precision published in 1954. It relates movement time to target distance and effective size. Applying it to interfaces provides a framework for examining pointing actions; it does not independently describe comprehension, trust or every factor affecting a decision.
Application in UX
Design targets that are easy to reach and avoid placing incompatible actions too close together. Check size, separation and precision on the intended devices. The law does not replace accessibility requirements.
Prioritise frequently used controls and review their actual interactive area rather than only the visible icon. Context matters: mouse, touch and other input methods have different conditions. Leave space between incompatible actions and check keyboard operation, whose accessibility cannot be inferred from target size.
Application in ecommerce
Size selectors, quantity controls and purchase buttons should be usable without unnecessary precision. Enlarging a button does not guarantee a conversion improvement.
On a product page, selecting variants and adding items to the basket should allow accurate pointing without accidentally activating another action. At checkout, separating back, remove and continue controls helps avoid mistakes. A larger button does not guarantee purchases: clear labels, sufficient information and behaviour matching shopper expectations are also necessary.
Practical example
Imagine a quantity selector where only the “+” symbol accepts a tap. Expanding its interactive area within the control and separating it from “−” may support easier use. Validate the proposal through mistaps and corrections, without inventing results.
Common mistakes
Treating the law as a recipe for enormous buttons ignores hierarchy and context. Another mistake is measuring the visible drawing when its clickable area is smaller. Avoid equating the model with automatic accessibility compliance or guaranteed conversion gains; observe selection errors and also consider comprehension and alternative interaction methods.