Fitts’ law isn’t actually a law but more of a principle. It states that the length of the time required for a person to move a cursor to a target area is a function of the distance to the target divided by the size of the target. Therefore, the longer the distance and the smaller the target’s size, the longer it takes.
In 1954, psychologist Paul Fitts, examining the human motor system, showed that the amount of time required to move to a target depends on the distance to it, yet relates inversely to its size. By his law, fast movements and small targets result in greater error rates, due to the speed-accuracy trade-off.
Fundamentally, it proves that it’s easier and faster for you to hit larger targets that are closer to you than those that are smaller and further away.
Take a look at the example below, the green represents the space that is easier for the thumb to travel to, while the orange and the red are not as easy to reach.
UX designers use Fitt’s law when creating user interfaces. Good UX designers ensure that any time they want users to interact with the software or the interface, they make it obvious. Targets are easily located and used. UX designers also know that the farther away the user’s mouse is and the farther away the target is, the longer it takes someone to move the cursor and click on the target.
We know that the size of the target matters. The larger the target, the easier it is to hit. This might lead the designer to think that it’s better if the button is bigger. But that isn’t always the case.
Good on-screen target placement is critical. As a designer, the physical locations of your target placements are extremely important. The Gutenberg diagram shows that users tend to move through screens from top-left to bottom-right. So consider placing what’s important like the CTA button in the parts of the screen users will tend to scan through.
