Make buttons larger

Digital interfaces require precise interactions—clicks, taps, and swipes. Designers optimize color contrasts, font sizes, and layouts. Yet many overlook a fundamental physical dimension: the motor movement itself. Users complain about cumbersome operations, accidental clicks, and fatiguing navigation. The question is: What physical laws govern the speed and precision of pointer movements? How can these be mathematically modeled—and what evidence exists to support them?

Studies

The Original Experiment with Pens and Discs

Paul Fitts conducted the foundational experiment on motor control at Ohio State University in 1954. Participants alternately tapped two metal discs with a stylus—sometimes positioned close together, sometimes far apart, and varying in size from large to small. Fitts systematically varied the distance (2 to 16 inches) and target width (0.25 to 2 inches), measuring movement time with a stopwatch. The surprising result: movement time precisely followed a logarithmic function. When distance doubled or target size halved, time increased by a constant factor. The formula MT = a + b × log₂(2D/W) explained 96% of the variance. Humans process motor information at approximately 10-12 bits per second—a constant that remained remarkably stable across different tasks and individuals.

Fitts' Law for Computer Mice

In 1997, Jean-Daniel Accot and Shumin Zhai at IBM Research tested whether Fitts' Law applies to modern computer interfaces. Twelve participants used a mouse to click on circular targets displayed on a screen. The researchers varied the distance from 64 to 512 pixels and the target size from 8 to 64 pixels. They also tested different input devices: mouse, trackball, and touchpad. The result: Fitts' Law held precisely for all devices, though with different constants. The mouse achieved 10.7 bits/second, while the trackball managed only 7.2 bits/second. Particularly striking: a target with an 8-pixel diameter at 512 pixels distance required an average of 1.2 seconds—an identical target at only 64 pixels distance required just 0.6 seconds. Halving the distance halved the interaction time, even 43 years after Fitts' original experiment.

Principle

Which principle for Customer Experience Design can be derived from this? Important actions require large, easily accessible click areas—interaction speed follows physical laws, not subjective preferences. Fitts's Law demonstrates that digital interface efficiency measurably depends on the size and position of interactive elements: doubling button size can reduce click time by approximately 15-20%. This becomes particularly critical on mobile devices, where small touch areas and poor positioning lead to frustration and abandonment, and for older users or people with motor impairments. However, this principle only applies to goal-directed actions—in exploratory interfaces or when deliberate slowing is desired (such as for irreversible actions), smaller elements can be appropriate. The following guidelines show how to implement this principle in practice.

Guidelines

Place primary actions large and close

Call-to-action buttons for important actions should be at least 44×44 pixels (touch) or 32×32 pixels (desktop) and positioned close to the likely cursor location. In forms, place the submit button directly below the last input field, not at the page margin. In modals, position the primary action at the bottom right, where the eye naturally ends. Interaction speed depends on the product of distance and inverse size—optimize both factors.

Use screen corners for main navigation

Corners and edges function as infinitely large targets—the cursor cannot move beyond them. This makes menus positioned in the upper left corner (Windows Start) or upper right corner (macOS system menu) optimally accessible. For web interfaces, this principle explains why logos belong in the upper left, shopping carts in the upper right, and footer links along the bottom edge. These positions dramatically reduce motor difficulty because users don't need to aim precisely. A link at the screen edge is effectively twice as easy to click as an identical link positioned in the middle of the screen.

Open context menus at cursor

Right-click menus should appear directly at the cursor position, not at a fixed location on screen. Every pixel of distance between the cursor and the first menu item costs time. Software like Adobe and Figma handles this correctly: the menu opens with the first item directly under the cursor. In contrast, menus that appear at the screen's center or at an object's edge force an unnecessary second movement. For frequently performed actions, this time loss accumulates into noticeable inefficiency.

Place destructive actions small and distant

Fitts' Law works bidirectionally: what is harder to reach is less likely to be clicked accidentally. Therefore, destructive actions like 'Delete', 'Cancel', or 'Close account' should be smaller and positioned farther from the primary flow. In dialogs, place the primary action large and on the right (aligned with reading flow), while keeping the destructive action small and on the left. In settings, position account deletion options small at the bottom of the page rather than prominently at the top. This increased motor difficulty encourages conscious action and reduces errors.