Applying Fitts’s Law to UX/UI Design

American psychologist Paul Morris Fitts, who worked at Ohio State University, conducted an experiment in 1954 that states a model of human movement while moving to a target. He proves that the time required to move to a target depends on the distance to it.

In simple terms, Fitts’ Law states that the bigger an object is and the closer it is to a person, the easier it will be for him to reach it.

Fitts’ law is centered around a mathematical equation

MT=a + b * log2(D/W + 1)

Yeah… sounds great. But how we profit from it?

Fitts’ law is widely applied in UX/UI design. Many companies worldwide increase sales conversation on their websites just by moving, for example, the “Add to cart” button to the right side of that site.

Fitts’ law can also be used to deliberately complicate the customer map, for example, by making the “Delete” button smaller. It can be not only buttons, but any other objects on a website page.

If a large button conflicts with the overall page design, then it is sufficient to enlarge not the button itself, but the clicking area.

The clicking zone (shown in a red square) is twice as large as the “Sign in” button. It is faster and more convenient for user (especially on mobile devices) to reach the target. ⬇️

Imagine, your cursor and attention are given to the logo of a particular website. Within seconds, a CTA pops up for user to be able to click on it ASAP. UX-analytics consider it using the Fitts’ Law. ⬇️

One more example is a dropdown menu. This is the fastes way to reach the feature. ⬇️

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