Fitts’s Law

Fitts’s Law is a principle in human-computer interaction that predicts the time required to move to a target based on the distance and size of the target. It states that the larger and closer a target is, the quicker it can be selected. This law is crucial for UI design, as it influences decisions about button sizes, spacing, and placement to ensure that interactive elements are easy to click or tap.

Fitts's Law is one of the few design principles with a mathematical formula behind it, making it unusually actionable. In practice it means: make your most important interactive elements (primary CTAs, nav items, submit buttons) large and positioned near where users' cursors or thumbs naturally rest. The corners of a screen on desktop are actually optimal targets per Fitts's Law because the cursor stops there naturally — which is why macOS puts the Apple menu in the top-left corner.

Mobile app designers apply Fitts's Law by placing primary actions (like 'Compose' in email apps) in the bottom-center of the screen — within easy thumb reach — while destructive actions like 'Delete' are placed far away, requiring deliberate movement to hit.