Fitts's Law

From Weekly I/O#34

Fitts’s Law: The time to acquire a target is a function of the distance to and size of the target in UI/UX.

Article: Fitts's Law: The Importance of Size and Distance in UI Design

Fitt's Law indicates that the level of difficulty to move a pointer to a target area can be formulated as the distance to the target divided by the size of the target. In other words, it will be harder to click a button on a website if our cursor is far from the button or the button size is small.

We can derive three simple design heuristics from this Law.

First, the pixel under the pointer/cursor is instantly usable without movement, called The Zero Point. Therefore, pop-up menus can often support the immediate selection of interactive elements more than dropdown menus since users don't have to move their pointer/cursor too much from the current position.

Second, the bigger target is always easier to click than a smaller one. When selecting options, pie menus can afford a larger target size than linear menus like vertical dropdown menus or horizontal top-level navigation. Moreover, travel distance is the same for all options in pie menus.

Third, the edges and the corners of the display are usually the easiest to select except for The Zero Point. We can see the edge of the screen as having an infinite depth since the user's pointer can be fixed at a point on the periphery of the screen.

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